SQL/JSON: add standard JSON constructor functions

This commit introduces the SQL/JSON standard-conforming constructors for
JSON types:

JSON_ARRAY()
JSON_ARRAYAGG()
JSON_OBJECT()
JSON_OBJECTAGG()

Most of the functionality was already present in PostgreSQL-specific
functions, but these include some new functionality such as the ability
to skip or include NULL values, and to allow duplicate keys or throw
error when they are found, as well as the standard specified syntax to
specify output type and format.

Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Amit Langote <amitlangote09@gmail.com>

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/CAF4Au4w2x-5LTnN_bxky-mq4=WOqsGsxSpENCzHRAzSnEd8+WQ@mail.gmail.com
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org

15 files changed, 2440 insertions, 125 deletions

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index c61f23c6c18..6c5a3780292 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -2279,6 +2279,97 @@ ExecInitExprRec(Expr *node, ExprState *state,
 				break;
 			}
 
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+
+				ExecInitExprRec(jve->raw_expr, state, resv, resnull);
+
+				if (jve->formatted_expr)
+				{
+					Datum	   *innermost_caseval = state->innermost_caseval;
+					bool	   *innermost_isnull = state->innermost_casenull;
+
+					state->innermost_caseval = resv;
+					state->innermost_casenull = resnull;
+
+					ExecInitExprRec(jve->formatted_expr, state, resv, resnull);
+
+					state->innermost_caseval = innermost_caseval;
+					state->innermost_casenull = innermost_isnull;
+				}
+				break;
+			}
+
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
+				List	   *args = ctor->args;
+				ListCell   *lc;
+				int			nargs = list_length(args);
+				int			argno = 0;
+
+				if (ctor->func)
+				{
+					ExecInitExprRec(ctor->func, state, resv, resnull);
+				}
+				else
+				{
+					JsonConstructorExprState *jcstate;
+
+					jcstate = palloc0(sizeof(JsonConstructorExprState));
+
+					scratch.opcode = EEOP_JSON_CONSTRUCTOR;
+					scratch.d.json_constructor.jcstate = jcstate;
+
+					jcstate->constructor = ctor;
+					jcstate->arg_values = (Datum *) palloc(sizeof(Datum) * nargs);
+					jcstate->arg_nulls = (bool *) palloc(sizeof(bool) * nargs);
+					jcstate->arg_types = (Oid *) palloc(sizeof(Oid) * nargs);
+					jcstate->nargs = nargs;
+
+					foreach(lc, args)
+					{
+						Expr	   *arg = (Expr *) lfirst(lc);
+
+						jcstate->arg_types[argno] = exprType((Node *) arg);
+
+						if (IsA(arg, Const))
+						{
+							/* Don't evaluate const arguments every round */
+							Const	   *con = (Const *) arg;
+
+							jcstate->arg_values[argno] = con->constvalue;
+							jcstate->arg_nulls[argno] = con->constisnull;
+						}
+						else
+						{
+							ExecInitExprRec(arg, state,
+											&jcstate->arg_values[argno],
+											&jcstate->arg_nulls[argno]);
+						}
+						argno++;
+					}
+
+					ExprEvalPushStep(state, &scratch);
+				}
+
+				if (ctor->coercion)
+				{
+					Datum	   *innermost_caseval = state->innermost_caseval;
+					bool	   *innermost_isnull = state->innermost_casenull;
+
+					state->innermost_caseval = resv;
+					state->innermost_casenull = resnull;
+
+					ExecInitExprRec(ctor->coercion, state, resv, resnull);
+
+					state->innermost_caseval = innermost_caseval;
+					state->innermost_casenull = innermost_isnull;
+				}
+			}
+			break;
+
 		case T_NullTest:
 			{
 				NullTest   *ntest = (NullTest *) node;
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index dd7d1af220a..a37ba4dd55b 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -71,6 +71,8 @@
 #include "utils/date.h"
 #include "utils/datum.h"
 #include "utils/expandedrecord.h"
+#include "utils/json.h"
+#include "utils/jsonb.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/timestamp.h"
@@ -474,6 +476,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		&&CASE_EEOP_SCALARARRAYOP,
 		&&CASE_EEOP_HASHED_SCALARARRAYOP,
 		&&CASE_EEOP_XMLEXPR,
+		&&CASE_EEOP_JSON_CONSTRUCTOR,
 		&&CASE_EEOP_AGGREF,
 		&&CASE_EEOP_GROUPING_FUNC,
 		&&CASE_EEOP_WINDOW_FUNC,
@@ -1511,6 +1514,13 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			EEO_NEXT();
 		}
 
+		EEO_CASE(EEOP_JSON_CONSTRUCTOR)
+		{
+			/* too complex for an inline implementation */
+			ExecEvalJsonConstructor(state, op, econtext);
+			EEO_NEXT();
+		}
+
 		EEO_CASE(EEOP_AGGREF)
 		{
 			/*
@@ -4437,3 +4447,43 @@ ExecAggPlainTransByRef(AggState *aggstate, AggStatePerTrans pertrans,
 
 	MemoryContextSwitchTo(oldContext);
 }
+
+/*
+ * Evaluate a JSON constructor expression.
+ */
+void
+ExecEvalJsonConstructor(ExprState *state, ExprEvalStep *op,
+						ExprContext *econtext)
+{
+	Datum		res;
+	JsonConstructorExprState *jcstate = op->d.json_constructor.jcstate;
+	JsonConstructorExpr *ctor = jcstate->constructor;
+	bool		is_jsonb = ctor->returning->format->format_type == JS_FORMAT_JSONB;
+	bool		isnull = false;
+
+	if (ctor->type == JSCTOR_JSON_ARRAY)
+		res = (is_jsonb ?
+			   jsonb_build_array_worker :
+			   json_build_array_worker) (jcstate->nargs,
+										 jcstate->arg_values,
+										 jcstate->arg_nulls,
+										 jcstate->arg_types,
+										 jcstate->constructor->absent_on_null);
+	else if (ctor->type == JSCTOR_JSON_OBJECT)
+		res = (is_jsonb ?
+			   jsonb_build_object_worker :
+			   json_build_object_worker) (jcstate->nargs,
+										  jcstate->arg_values,
+										  jcstate->arg_nulls,
+										  jcstate->arg_types,
+										  jcstate->constructor->absent_on_null,
+										  jcstate->constructor->unique);
+	else
+	{
+		res = (Datum) 0;
+		elog(ERROR, "invalid JsonConstructorExpr type %d", ctor->type);
+	}
+
+	*op->resvalue = res;
+	*op->resnull = isnull;
+}
diff --git a/src/backend/jit/llvm/llvmjit_expr.c b/src/backend/jit/llvm/llvmjit_expr.c
index 1c722c79552..12d39394b31 100644
--- a/src/backend/jit/llvm/llvmjit_expr.c
+++ b/src/backend/jit/llvm/llvmjit_expr.c
@@ -1842,6 +1842,12 @@ llvm_compile_expr(ExprState *state)
 				LLVMBuildBr(b, opblocks[opno + 1]);
 				break;
 
+			case EEOP_JSON_CONSTRUCTOR:
+				build_EvalXFunc(b, mod, "ExecEvalJsonConstructor",
+								v_state, op, v_econtext);
+				LLVMBuildBr(b, opblocks[opno + 1]);
+				break;
+
 			case EEOP_AGGREF:
 				{
 					LLVMValueRef v_aggno;
diff --git a/src/backend/jit/llvm/llvmjit_types.c b/src/backend/jit/llvm/llvmjit_types.c
index 876fb640294..315eeb11720 100644
--- a/src/backend/jit/llvm/llvmjit_types.c
+++ b/src/backend/jit/llvm/llvmjit_types.c
@@ -132,6 +132,7 @@ void	   *referenced_functions[] =
 	ExecEvalSysVar,
 	ExecEvalWholeRowVar,
 	ExecEvalXmlExpr,
+	ExecEvalJsonConstructor,
 	MakeExpandedObjectReadOnlyInternal,
 	slot_getmissingattrs,
 	slot_getsomeattrs_int,
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 216383ca239..23c71528065 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -19,6 +19,7 @@
 #include "catalog/pg_type.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
+#include "utils/errcodes.h"
 #include "utils/lsyscache.h"
 
 
@@ -825,3 +826,71 @@ makeVacuumRelation(RangeVar *relation, Oid oid, List *va_cols)
 	v->va_cols = va_cols;
 	return v;
 }
+
+/*
+ * makeJsonFormat -
+ *	  creates a JsonFormat node
+ */
+JsonFormat *
+makeJsonFormat(JsonFormatType type, JsonEncoding encoding, int location)
+{
+	JsonFormat *jf = makeNode(JsonFormat);
+
+	jf->format_type = type;
+	jf->encoding = encoding;
+	jf->location = location;
+
+	return jf;
+}
+
+/*
+ * makeJsonValueExpr -
+ *	  creates a JsonValueExpr node
+ */
+JsonValueExpr *
+makeJsonValueExpr(Expr *expr, JsonFormat *format)
+{
+	JsonValueExpr *jve = makeNode(JsonValueExpr);
+
+	jve->raw_expr = expr;
+	jve->formatted_expr = NULL;
+	jve->format = format;
+
+	return jve;
+}
+
+/*
+ * makeJsonEncoding -
+ *	  converts JSON encoding name to enum JsonEncoding
+ */
+JsonEncoding
+makeJsonEncoding(char *name)
+{
+	if (!pg_strcasecmp(name, "utf8"))
+		return JS_ENC_UTF8;
+	if (!pg_strcasecmp(name, "utf16"))
+		return JS_ENC_UTF16;
+	if (!pg_strcasecmp(name, "utf32"))
+		return JS_ENC_UTF32;
+
+	ereport(ERROR,
+			errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+			errmsg("unrecognized JSON encoding: %s", name));
+
+	return JS_ENC_DEFAULT;
+}
+
+/*
+ * makeJsonKeyValue -
+ *	  creates a JsonKeyValue node
+ */
+Node *
+makeJsonKeyValue(Node *key, Node *value)
+{
+	JsonKeyValue *n = makeNode(JsonKeyValue);
+
+	n->key = (Expr *) key;
+	n->value = castNode(JsonValueExpr, value);
+
+	return (Node *) n;
+}
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index dc8415a693c..69907fbcde8 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -249,6 +249,18 @@ exprType(const Node *expr)
 		case T_PlaceHolderVar:
 			type = exprType((Node *) ((const PlaceHolderVar *) expr)->phexpr);
 			break;
+		case T_JsonValueExpr:
+			{
+				const JsonValueExpr *jve = (const JsonValueExpr *) expr;
+
+				type = exprType((Node *)
+								(jve->formatted_expr ? jve->formatted_expr :
+								 jve->raw_expr));
+			}
+			break;
+		case T_JsonConstructorExpr:
+			type = ((const JsonConstructorExpr *) expr)->returning->typid;
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			type = InvalidOid;	/* keep compiler quiet */
@@ -479,6 +491,10 @@ exprTypmod(const Node *expr)
 			return ((const SetToDefault *) expr)->typeMod;
 		case T_PlaceHolderVar:
 			return exprTypmod((Node *) ((const PlaceHolderVar *) expr)->phexpr);
+		case T_JsonValueExpr:
+			return exprTypmod((Node *) ((const JsonValueExpr *) expr)->formatted_expr);
+		case T_JsonConstructorExpr:
+			return -1;			/* XXX maybe expr->returning->typmod? */
 		default:
 			break;
 	}
@@ -954,6 +970,19 @@ exprCollation(const Node *expr)
 		case T_PlaceHolderVar:
 			coll = exprCollation((Node *) ((const PlaceHolderVar *) expr)->phexpr);
 			break;
+		case T_JsonValueExpr:
+			coll = exprCollation((Node *) ((const JsonValueExpr *) expr)->formatted_expr);
+			break;
+		case T_JsonConstructorExpr:
+			{
+				const JsonConstructorExpr *ctor = (const JsonConstructorExpr *) expr;
+
+				if (ctor->coercion)
+					coll = exprCollation((Node *) ctor->coercion);
+				else
+					coll = InvalidOid;
+			}
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			coll = InvalidOid;	/* keep compiler quiet */
@@ -1161,6 +1190,21 @@ exprSetCollation(Node *expr, Oid collation)
 			/* NextValueExpr's result is an integer type ... */
 			Assert(!OidIsValid(collation)); /* ... so never set a collation */
 			break;
+		case T_JsonValueExpr:
+			exprSetCollation((Node *) ((JsonValueExpr *) expr)->formatted_expr,
+							 collation);
+			break;
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *ctor = (JsonConstructorExpr *) expr;
+
+				if (ctor->coercion)
+					exprSetCollation((Node *) ctor->coercion, collation);
+				else
+					Assert(!OidIsValid(collation)); /* result is always a
+													 * json[b] type */
+			}
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			break;
@@ -1603,6 +1647,12 @@ exprLocation(const Node *expr)
 		case T_PartitionRangeDatum:
 			loc = ((const PartitionRangeDatum *) expr)->location;
 			break;
+		case T_JsonValueExpr:
+			loc = exprLocation((Node *) ((const JsonValueExpr *) expr)->raw_expr);
+			break;
+		case T_JsonConstructorExpr:
+			loc = ((const JsonConstructorExpr *) expr)->location;
+			break;
 		default:
 			/* for any other node type it's just unknown... */
 			loc = -1;
@@ -2334,6 +2384,28 @@ expression_tree_walker_impl(Node *node,
 					return true;
 			}
 			break;
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+
+				if (WALK(jve->raw_expr))
+					return true;
+				if (WALK(jve->formatted_expr))
+					return true;
+			}
+			break;
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
+
+				if (WALK(ctor->args))
+					return true;
+				if (WALK(ctor->func))
+					return true;
+				if (WALK(ctor->coercion))
+					return true;
+			}
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));
@@ -2664,6 +2736,7 @@ expression_tree_mutator_impl(Node *node,
 		case T_RangeTblRef:
 		case T_SortGroupClause:
 		case T_CTESearchClause:
+		case T_JsonFormat:
 			return (Node *) copyObject(node);
 		case T_WithCheckOption:
 			{
@@ -3307,6 +3380,41 @@ expression_tree_mutator_impl(Node *node,
 				return (Node *) newnode;
 			}
 			break;
+		case T_JsonReturning:
+			{
+				JsonReturning *jr = (JsonReturning *) node;
+				JsonReturning *newnode;
+
+				FLATCOPY(newnode, jr, JsonReturning);
+				MUTATE(newnode->format, jr->format, JsonFormat *);
+
+				return (Node *) newnode;
+			}
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+				JsonValueExpr *newnode;
+
+				FLATCOPY(newnode, jve, JsonValueExpr);
+				MUTATE(newnode->raw_expr, jve->raw_expr, Expr *);
+				MUTATE(newnode->formatted_expr, jve->formatted_expr, Expr *);
+				MUTATE(newnode->format, jve->format, JsonFormat *);
+
+				return (Node *) newnode;
+			}
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *jve = (JsonConstructorExpr *) node;
+				JsonConstructorExpr *newnode;
+
+				FLATCOPY(newnode, jve, JsonConstructorExpr);
+				MUTATE(newnode->args, jve->args, List *);
+				MUTATE(newnode->func, jve->func, Expr *);
+				MUTATE(newnode->coercion, jve->coercion, Expr *);
+				MUTATE(newnode->returning, jve->returning, JsonReturning *);
+
+				return (Node *) newnode;
+			}
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));
@@ -3578,6 +3686,7 @@ raw_expression_tree_walker_impl(Node *node,
 		case T_ParamRef:
 		case T_A_Const:
 		case T_A_Star:
+		case T_JsonFormat:
 			/* primitive node types with no subnodes */
 			break;
 		case T_Alias:
@@ -4040,6 +4149,118 @@ raw_expression_tree_walker_impl(Node *node,
 		case T_CommonTableExpr:
 			/* search_clause and cycle_clause are not interesting here */
 			return WALK(((CommonTableExpr *) node)->ctequery);
+		case T_JsonReturning:
+			return WALK(((JsonReturning *) node)->format);
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+
+				if (WALK(jve->raw_expr))
+					return true;
+				if (WALK(jve->formatted_expr))
+					return true;
+				if (WALK(jve->format))
+					return true;
+			}
+			break;
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
+
+				if (WALK(ctor->args))
+					return true;
+				if (WALK(ctor->func))
+					return true;
+				if (WALK(ctor->coercion))
+					return true;
+				if (WALK(ctor->returning))
+					return true;
+			}
+			break;
+		case T_JsonOutput:
+			{
+				JsonOutput *out = (JsonOutput *) node;
+
+				if (WALK(out->typeName))
+					return true;
+				if (WALK(out->returning))
+					return true;
+			}
+			break;
+		case T_JsonKeyValue:
+			{
+				JsonKeyValue *jkv = (JsonKeyValue *) node;
+
+				if (WALK(jkv->key))
+					return true;
+				if (WALK(jkv->value))
+					return true;
+			}
+			break;
+		case T_JsonObjectConstructor:
+			{
+				JsonObjectConstructor *joc = (JsonObjectConstructor *) node;
+
+				if (WALK(joc->output))
+					return true;
+				if (WALK(joc->exprs))
+					return true;
+			}
+			break;
+		case T_JsonArrayConstructor:
+			{
+				JsonArrayConstructor *jac = (JsonArrayConstructor *) node;
+
+				if (WALK(jac->output))
+					return true;
+				if (WALK(jac->exprs))
+					return true;
+			}
+			break;
+		case T_JsonAggConstructor:
+			{
+				JsonAggConstructor *ctor = (JsonAggConstructor *) node;
+
+				if (WALK(ctor->output))
+					return true;
+				if (WALK(ctor->agg_order))
+					return true;
+				if (WALK(ctor->agg_filter))
+					return true;
+				if (WALK(ctor->over))
+					return true;
+			}
+			break;
+		case T_JsonObjectAgg:
+			{
+				JsonObjectAgg *joa = (JsonObjectAgg *) node;
+
+				if (WALK(joa->constructor))
+					return true;
+				if (WALK(joa->arg))
+					return true;
+			}
+			break;
+		case T_JsonArrayAgg:
+			{
+				JsonArrayAgg *jaa = (JsonArrayAgg *) node;
+
+				if (WALK(jaa->constructor))
+					return true;
+				if (WALK(jaa->arg))
+					return true;
+			}
+			break;
+		case T_JsonArrayQueryConstructor:
+			{
+				JsonArrayQueryConstructor *jaqc = (JsonArrayQueryConstructor *) node;
+
+				if (WALK(jaqc->output))
+					return true;
+				if (WALK(jaqc->query))
+					return true;
+			}
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index fc245c60e41..a9c7bc342ec 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -51,6 +51,8 @@
 #include "utils/builtins.h"
 #include "utils/datum.h"
 #include "utils/fmgroids.h"
+#include "utils/json.h"
+#include "utils/jsonb.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/syscache.h"
@@ -383,6 +385,33 @@ contain_mutable_functions_walker(Node *node, void *context)
 								context))
 		return true;
 
+	if (IsA(node, JsonConstructorExpr))
+	{
+		const JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
+		ListCell   *lc;
+		bool		is_jsonb;
+
+		is_jsonb = ctor->returning->format->format_type == JS_FORMAT_JSONB;
+
+		/*
+		 * Check argument_type => json[b] conversions specifically.  We still
+		 * recurse to check 'args' below, but here we want to specifically
+		 * check whether or not the emitted clause would fail to be immutable
+		 * because of TimeZone, for example.
+		 */
+		foreach(lc, ctor->args)
+		{
+			Oid			typid = exprType(lfirst(lc));
+
+			if (is_jsonb ?
+				!to_jsonb_is_immutable(typid) :
+				!to_json_is_immutable(typid))
+				return true;
+		}
+
+		/* Check all subnodes */
+	}
+
 	if (IsA(node, NextValueExpr))
 	{
 		/* NextValueExpr is volatile */
@@ -2786,6 +2815,32 @@ eval_const_expressions_mutator(Node *node,
 				}
 				break;
 			}
+
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+				Node	   *raw;
+
+				raw = eval_const_expressions_mutator((Node *) jve->raw_expr,
+													 context);
+				if (raw && IsA(raw, Const))
+				{
+					Node	   *formatted;
+					Node	   *save_case_val = context->case_val;
+
+					context->case_val = raw;
+
+					formatted = eval_const_expressions_mutator((Node *) jve->formatted_expr,
+															   context);
+
+					context->case_val = save_case_val;
+
+					if (formatted && IsA(formatted, Const))
+						return formatted;
+				}
+				break;
+			}
+
 		case T_SubPlan:
 		case T_AlternativeSubPlan:
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index efe88ccf9da..54c7896a6c6 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -644,6 +644,22 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <defelt>		hash_partbound_elem
 
 
+%type <node>		json_format_clause_opt
+					json_value_expr
+					json_output_clause_opt
+					json_name_and_value
+					json_aggregate_func
+
+%type <list>		json_name_and_value_list
+					json_value_expr_list
+					json_array_aggregate_order_by_clause_opt
+
+%type <ival>		json_encoding_clause_opt
+
+%type <boolean>		json_key_uniqueness_constraint_opt
+					json_object_constructor_null_clause_opt
+					json_array_constructor_null_clause_opt
+
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
  * They must be listed first so that their numeric codes do not depend on
@@ -669,7 +685,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
  */
 
 /* ordinary key words in alphabetical order */
-%token <keyword> ABORT_P ABSOLUTE_P ACCESS ACTION ADD_P ADMIN AFTER
+%token <keyword> ABORT_P ABSENT ABSOLUTE_P ACCESS ACTION ADD_P ADMIN AFTER
 	AGGREGATE ALL ALSO ALTER ALWAYS ANALYSE ANALYZE AND ANY ARRAY AS ASC
 	ASENSITIVE ASSERTION ASSIGNMENT ASYMMETRIC ATOMIC AT ATTACH ATTRIBUTE AUTHORIZATION
 
@@ -695,7 +711,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	EXTENSION EXTERNAL EXTRACT
 
 	FALSE_P FAMILY FETCH FILTER FINALIZE FIRST_P FLOAT_P FOLLOWING FOR
-	FORCE FOREIGN FORWARD FREEZE FROM FULL FUNCTION FUNCTIONS
+	FORCE FOREIGN FORMAT FORWARD FREEZE FROM FULL FUNCTION FUNCTIONS
 
 	GENERATED GLOBAL GRANT GRANTED GREATEST GROUP_P GROUPING GROUPS
 
@@ -706,9 +722,9 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
 
-	JOIN
+	JOIN JSON JSON_ARRAY JSON_ARRAYAGG JSON_OBJECT JSON_OBJECTAGG
 
-	KEY
+	KEY KEYS
 
 	LABEL LANGUAGE LARGE_P LAST_P LATERAL_P
 	LEADING LEAKPROOF LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL
@@ -772,9 +788,10 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
  * NOT_LA exists so that productions such as NOT LIKE can be given the same
  * precedence as LIKE; otherwise they'd effectively have the same precedence
  * as NOT, at least with respect to their left-hand subexpression.
- * NULLS_LA and WITH_LA are needed to make the grammar LALR(1).
+ * FORMAT_LA, NULLS_LA, WITH_LA, and WITHOUT_LA are needed to make the grammar
+ * LALR(1).
  */
-%token		NOT_LA NULLS_LA WITH_LA
+%token		FORMAT_LA NOT_LA NULLS_LA WITH_LA WITHOUT_LA
 
 /*
  * The grammar likewise thinks these tokens are keywords, but they are never
@@ -792,6 +809,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 /* Precedence: lowest to highest */
 %nonassoc	SET				/* see relation_expr_opt_alias */
+%right		FORMAT
 %left		UNION EXCEPT
 %left		INTERSECT
 %left		OR
@@ -11698,6 +11716,7 @@ utility_option_elem:
 utility_option_name:
 			NonReservedWord							{ $$ = $1; }
 			| analyze_keyword						{ $$ = "analyze"; }
+			| FORMAT_LA								{ $$ = "format"; }
 		;
 
 utility_option_arg:
@@ -15185,6 +15204,16 @@ func_expr: func_application within_group_clause filter_clause over_clause
 					n->over = $4;
 					$$ = (Node *) n;
 				}
+			| json_aggregate_func filter_clause over_clause
+				{
+					JsonAggConstructor *n = IsA($1, JsonObjectAgg) ?
+						((JsonObjectAgg *) $1)->constructor :
+						((JsonArrayAgg *) $1)->constructor;
+
+					n->agg_filter = $2;
+					n->over = $3;
+					$$ = (Node *) $1;
+				}
 			| func_expr_common_subexpr
 				{ $$ = $1; }
 		;
@@ -15198,6 +15227,7 @@ func_expr: func_application within_group_clause filter_clause over_clause
 func_expr_windowless:
 			func_application						{ $$ = $1; }
 			| func_expr_common_subexpr				{ $$ = $1; }
+			| json_aggregate_func					{ $$ = $1; }
 		;
 
 /*
@@ -15543,6 +15573,79 @@ func_expr_common_subexpr:
 					n->location = @1;
 					$$ = (Node *) n;
 				}
+			| JSON_OBJECT '(' func_arg_list ')'
+				{
+					/* Support for legacy (non-standard) json_object() */
+					$$ = (Node *) makeFuncCall(SystemFuncName("json_object"),
+											   $3, COERCE_EXPLICIT_CALL, @1);
+				}
+			| JSON_OBJECT '(' json_name_and_value_list
+				json_object_constructor_null_clause_opt
+				json_key_uniqueness_constraint_opt
+				json_output_clause_opt ')'
+				{
+					JsonObjectConstructor *n = makeNode(JsonObjectConstructor);
+
+					n->exprs = $3;
+					n->absent_on_null = $4;
+					n->unique = $5;
+					n->output = (JsonOutput *) $6;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
+			| JSON_OBJECT '(' json_output_clause_opt ')'
+				{
+					JsonObjectConstructor *n = makeNode(JsonObjectConstructor);
+
+					n->exprs = NULL;
+					n->absent_on_null = false;
+					n->unique = false;
+					n->output = (JsonOutput *) $3;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
+			| JSON_ARRAY '('
+				json_value_expr_list
+				json_array_constructor_null_clause_opt
+				json_output_clause_opt
+			')'
+				{
+					JsonArrayConstructor *n = makeNode(JsonArrayConstructor);
+
+					n->exprs = $3;
+					n->absent_on_null = $4;
+					n->output = (JsonOutput *) $5;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
+			| JSON_ARRAY '('
+				select_no_parens
+				json_format_clause_opt
+				/* json_array_constructor_null_clause_opt */
+				json_output_clause_opt
+			')'
+				{
+					JsonArrayQueryConstructor *n = makeNode(JsonArrayQueryConstructor);
+
+					n->query = $3;
+					n->format = (JsonFormat *) $4;
+					n->absent_on_null = true;	/* XXX */
+					n->output = (JsonOutput *) $5;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
+			| JSON_ARRAY '('
+				json_output_clause_opt
+			')'
+				{
+					JsonArrayConstructor *n = makeNode(JsonArrayConstructor);
+
+					n->exprs = NIL;
+					n->absent_on_null = true;
+					n->output = (JsonOutput *) $3;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
 		;
 
 /*
@@ -16267,6 +16370,132 @@ opt_asymmetric: ASYMMETRIC
 			| /*EMPTY*/
 		;
 
+/* SQL/JSON support */
+json_value_expr:
+			a_expr json_format_clause_opt
+			{
+				$$ = (Node *) makeJsonValueExpr((Expr *) $1, castNode(JsonFormat, $2));
+			}
+		;
+
+json_format_clause_opt:
+			FORMAT_LA JSON json_encoding_clause_opt
+				{
+					$$ = (Node *) makeJsonFormat(JS_FORMAT_JSON, $3, @1);
+				}
+			| /* EMPTY */
+				{
+					$$ = (Node *) makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, -1);
+				}
+		;
+
+json_encoding_clause_opt:
+			ENCODING name					{ $$ = makeJsonEncoding($2); }
+			| /* EMPTY */					{ $$ = JS_ENC_DEFAULT; }
+		;
+
+json_output_clause_opt:
+			RETURNING Typename json_format_clause_opt
+				{
+					JsonOutput *n = makeNode(JsonOutput);
+
+					n->typeName = $2;
+					n->returning = makeNode(JsonReturning);
+					n->returning->format = (JsonFormat *) $3;
+					$$ = (Node *) n;
+				}
+			| /* EMPTY */							{ $$ = NULL; }
+		;
+
+/* KEYS is a noise word here */
+json_key_uniqueness_constraint_opt:
+			WITH UNIQUE KEYS				{ $$ = true; }
+			| WITH UNIQUE				    { $$ = true; }
+			| WITHOUT_LA UNIQUE KEYS		{ $$ = false; }
+			| WITHOUT_LA UNIQUE			    { $$ = false; }
+			| /* EMPTY */ 					{ $$ = false; }
+		;
+
+json_name_and_value_list:
+			json_name_and_value
+				{ $$ = list_make1($1); }
+			| json_name_and_value_list ',' json_name_and_value
+				{ $$ = lappend($1, $3); }
+		;
+
+json_name_and_value:
+/* Supporting this syntax seems to require major surgery
+			KEY c_expr VALUE_P json_value_expr
+				{ $$ = makeJsonKeyValue($2, $4); }
+			|
+*/
+			c_expr VALUE_P json_value_expr
+				{ $$ = makeJsonKeyValue($1, $3); }
+			|
+			a_expr ':' json_value_expr
+				{ $$ = makeJsonKeyValue($1, $3); }
+		;
+
+/* empty means false for objects, true for arrays */
+json_object_constructor_null_clause_opt:
+			NULL_P ON NULL_P					{ $$ = false; }
+			| ABSENT ON NULL_P					{ $$ = true; }
+			| /* EMPTY */						{ $$ = false; }
+		;
+
+json_array_constructor_null_clause_opt:
+			NULL_P ON NULL_P						{ $$ = false; }
+			| ABSENT ON NULL_P						{ $$ = true; }
+			| /* EMPTY */							{ $$ = true; }
+		;
+
+json_value_expr_list:
+			json_value_expr								{ $$ = list_make1($1); }
+			| json_value_expr_list ',' json_value_expr	{ $$ = lappend($1, $3);}
+		;
+
+json_aggregate_func:
+			JSON_OBJECTAGG '('
+				json_name_and_value
+				json_object_constructor_null_clause_opt
+				json_key_uniqueness_constraint_opt
+				json_output_clause_opt
+			')'
+				{
+					JsonObjectAgg *n = makeNode(JsonObjectAgg);
+
+					n->arg = (JsonKeyValue *) $3;
+					n->absent_on_null = $4;
+					n->unique = $5;
+					n->constructor = makeNode(JsonAggConstructor);
+					n->constructor->output = (JsonOutput *) $6;
+					n->constructor->agg_order = NULL;
+					n->constructor->location = @1;
+					$$ = (Node *) n;
+				}
+			| JSON_ARRAYAGG '('
+				json_value_expr
+				json_array_aggregate_order_by_clause_opt
+				json_array_constructor_null_clause_opt
+				json_output_clause_opt
+			')'
+				{
+					JsonArrayAgg *n = makeNode(JsonArrayAgg);
+
+					n->arg = (JsonValueExpr *) $3;
+					n->absent_on_null = $5;
+					n->constructor = makeNode(JsonAggConstructor);
+					n->constructor->agg_order = $4;
+					n->constructor->output = (JsonOutput *) $6;
+					n->constructor->location = @1;
+					$$ = (Node *) n;
+				}
+		;
+
+json_array_aggregate_order_by_clause_opt:
+			ORDER BY sortby_list					{ $$ = $3; }
+			| /* EMPTY */							{ $$ = NIL; }
+		;
 
 /*****************************************************************************
  *
@@ -16718,6 +16947,7 @@ BareColLabel:	IDENT								{ $$ = $1; }
  */
 unreserved_keyword:
 			  ABORT_P
+			| ABSENT
 			| ABSOLUTE_P
 			| ACCESS
 			| ACTION
@@ -16814,6 +17044,7 @@ unreserved_keyword:
 			| FIRST_P
 			| FOLLOWING
 			| FORCE
+			| FORMAT
 			| FORWARD
 			| FUNCTION
 			| FUNCTIONS
@@ -16846,7 +17077,9 @@ unreserved_keyword:
 			| INSTEAD
 			| INVOKER
 			| ISOLATION
+			| JSON
 			| KEY
+			| KEYS
 			| LABEL
 			| LANGUAGE
 			| LARGE_P
@@ -17058,6 +17291,10 @@ col_name_keyword:
 			| INT_P
 			| INTEGER
 			| INTERVAL
+			| JSON_ARRAY
+			| JSON_ARRAYAGG
+			| JSON_OBJECT
+			| JSON_OBJECTAGG
 			| LEAST
 			| NATIONAL
 			| NCHAR
@@ -17227,6 +17464,7 @@ reserved_keyword:
  */
 bare_label_keyword:
 			  ABORT_P
+			| ABSENT
 			| ABSOLUTE_P
 			| ACCESS
 			| ACTION
@@ -17366,6 +17604,7 @@ bare_label_keyword:
 			| FOLLOWING
 			| FORCE
 			| FOREIGN
+			| FORMAT
 			| FORWARD
 			| FREEZE
 			| FULL
@@ -17411,7 +17650,13 @@ bare_label_keyword:
 			| IS
 			| ISOLATION
 			| JOIN
+			| JSON
+			| JSON_ARRAY
+			| JSON_ARRAYAGG
+			| JSON_OBJECT
+			| JSON_OBJECTAGG
 			| KEY
+			| KEYS
 			| LABEL
 			| LANGUAGE
 			| LARGE_P
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 23314175522..a134878b1e9 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -15,6 +15,8 @@
 
 #include "postgres.h"
 
+#include "catalog/pg_aggregate.h"
+#include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
 #include "miscadmin.h"
@@ -34,6 +36,7 @@
 #include "parser/parse_type.h"
 #include "utils/builtins.h"
 #include "utils/date.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/timestamp.h"
 #include "utils/xml.h"
@@ -72,6 +75,14 @@ static Node *transformWholeRowRef(ParseState *pstate,
 static Node *transformIndirection(ParseState *pstate, A_Indirection *ind);
 static Node *transformTypeCast(ParseState *pstate, TypeCast *tc);
 static Node *transformCollateClause(ParseState *pstate, CollateClause *c);
+static Node *transformJsonObjectConstructor(ParseState *pstate,
+											JsonObjectConstructor *ctor);
+static Node *transformJsonArrayConstructor(ParseState *pstate,
+										   JsonArrayConstructor *ctor);
+static Node *transformJsonArrayQueryConstructor(ParseState *pstate,
+												JsonArrayQueryConstructor *ctor);
+static Node *transformJsonObjectAgg(ParseState *pstate, JsonObjectAgg *agg);
+static Node *transformJsonArrayAgg(ParseState *pstate, JsonArrayAgg *agg);
 static Node *make_row_comparison_op(ParseState *pstate, List *opname,
 									List *largs, List *rargs, int location);
 static Node *make_row_distinct_op(ParseState *pstate, List *opname,
@@ -294,6 +305,26 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 				break;
 			}
 
+		case T_JsonObjectConstructor:
+			result = transformJsonObjectConstructor(pstate, (JsonObjectConstructor *) expr);
+			break;
+
+		case T_JsonArrayConstructor:
+			result = transformJsonArrayConstructor(pstate, (JsonArrayConstructor *) expr);
+			break;
+
+		case T_JsonArrayQueryConstructor:
+			result = transformJsonArrayQueryConstructor(pstate, (JsonArrayQueryConstructor *) expr);
+			break;
+
+		case T_JsonObjectAgg:
+			result = transformJsonObjectAgg(pstate, (JsonObjectAgg *) expr);
+			break;
+
+		case T_JsonArrayAgg:
+			result = transformJsonArrayAgg(pstate, (JsonArrayAgg *) expr);
+			break;
+
 		default:
 			/* should not reach here */
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
@@ -3047,3 +3078,742 @@ ParseExprKindName(ParseExprKind exprKind)
 	}
 	return "unrecognized expression kind";
 }
+
+/*
+ * Make string Const node from JSON encoding name.
+ *
+ * UTF8 is default encoding.
+ */
+static Const *
+getJsonEncodingConst(JsonFormat *format)
+{
+	JsonEncoding encoding;
+	const char *enc;
+	Name		encname = palloc(sizeof(NameData));
+
+	if (!format ||
+		format->format_type == JS_FORMAT_DEFAULT ||
+		format->encoding == JS_ENC_DEFAULT)
+		encoding = JS_ENC_UTF8;
+	else
+		encoding = format->encoding;
+
+	switch (encoding)
+	{
+		case JS_ENC_UTF16:
+			enc = "UTF16";
+			break;
+		case JS_ENC_UTF32:
+			enc = "UTF32";
+			break;
+		case JS_ENC_UTF8:
+			enc = "UTF8";
+			break;
+		default:
+			elog(ERROR, "invalid JSON encoding: %d", encoding);
+			break;
+	}
+
+	namestrcpy(encname, enc);
+
+	return makeConst(NAMEOID, -1, InvalidOid, NAMEDATALEN,
+					 NameGetDatum(encname), false, false);
+}
+
+/*
+ * Make bytea => text conversion using specified JSON format encoding.
+ */
+static Node *
+makeJsonByteaToTextConversion(Node *expr, JsonFormat *format, int location)
+{
+	Const	   *encoding = getJsonEncodingConst(format);
+	FuncExpr   *fexpr = makeFuncExpr(F_CONVERT_FROM, TEXTOID,
+									 list_make2(expr, encoding),
+									 InvalidOid, InvalidOid,
+									 COERCE_EXPLICIT_CALL);
+
+	fexpr->location = location;
+
+	return (Node *) fexpr;
+}
+
+/*
+ * Make CaseTestExpr node.
+ */
+static Node *
+makeCaseTestExpr(Node *expr)
+{
+	CaseTestExpr *placeholder = makeNode(CaseTestExpr);
+
+	placeholder->typeId = exprType(expr);
+	placeholder->typeMod = exprTypmod(expr);
+	placeholder->collation = exprCollation(expr);
+
+	return (Node *) placeholder;
+}
+
+/*
+ * Transform JSON value expression using specified input JSON format or
+ * default format otherwise.
+ */
+static Node *
+transformJsonValueExpr(ParseState *pstate, JsonValueExpr *ve,
+					   JsonFormatType default_format)
+{
+	Node	   *expr = transformExprRecurse(pstate, (Node *) ve->raw_expr);
+	Node	   *rawexpr;
+	JsonFormatType format;
+	Oid			exprtype;
+	int			location;
+	char		typcategory;
+	bool		typispreferred;
+
+	/*
+	 * Using JSON_VALUE here is slightly bogus: perhaps we need to be passed a
+	 * JsonConstructorType so that we can use one of JSON_OBJECTAGG, etc.
+	 */
+	if (exprType(expr) == UNKNOWNOID)
+		expr = coerce_to_specific_type(pstate, expr, TEXTOID, "JSON_VALUE");
+
+	rawexpr = expr;
+	exprtype = exprType(expr);
+	location = exprLocation(expr);
+
+	get_type_category_preferred(exprtype, &typcategory, &typispreferred);
+
+	if (ve->format->format_type != JS_FORMAT_DEFAULT)
+	{
+		if (ve->format->encoding != JS_ENC_DEFAULT && exprtype != BYTEAOID)
+			ereport(ERROR,
+					errcode(ERRCODE_DATATYPE_MISMATCH),
+					errmsg("JSON ENCODING clause is only allowed for bytea input type"),
+					parser_errposition(pstate, ve->format->location));
+
+		if (exprtype == JSONOID || exprtype == JSONBOID)
+		{
+			format = JS_FORMAT_DEFAULT; /* do not format json[b] types */
+			ereport(WARNING,
+					errmsg("FORMAT JSON has no effect for json and jsonb types"),
+					parser_errposition(pstate, ve->format->location));
+		}
+		else
+			format = ve->format->format_type;
+	}
+	else if (exprtype == JSONOID || exprtype == JSONBOID)
+		format = JS_FORMAT_DEFAULT; /* do not format json[b] types */
+	else
+		format = default_format;
+
+	if (format != JS_FORMAT_DEFAULT)
+	{
+		Oid			targettype = format == JS_FORMAT_JSONB ? JSONBOID : JSONOID;
+		Node	   *orig = makeCaseTestExpr(expr);
+		Node	   *coerced;
+
+		expr = orig;
+
+		if (exprtype != BYTEAOID && typcategory != TYPCATEGORY_STRING)
+			ereport(ERROR,
+					errcode(ERRCODE_DATATYPE_MISMATCH),
+					errmsg(ve->format->format_type == JS_FORMAT_DEFAULT ?
+						   "cannot use non-string types with implicit FORMAT JSON clause" :
+						   "cannot use non-string types with explicit FORMAT JSON clause"),
+					parser_errposition(pstate, ve->format->location >= 0 ?
+									   ve->format->location : location));
+
+		/* Convert encoded JSON text from bytea. */
+		if (format == JS_FORMAT_JSON && exprtype == BYTEAOID)
+		{
+			expr = makeJsonByteaToTextConversion(expr, ve->format, location);
+			exprtype = TEXTOID;
+		}
+
+		/* Try to coerce to the target type. */
+		coerced = coerce_to_target_type(pstate, expr, exprtype,
+										targettype, -1,
+										COERCION_EXPLICIT,
+										COERCE_EXPLICIT_CAST,
+										location);
+
+		if (!coerced)
+		{
+			/* If coercion failed, use to_json()/to_jsonb() functions. */
+			Oid			fnoid = targettype == JSONOID ? F_TO_JSON : F_TO_JSONB;
+			FuncExpr   *fexpr = makeFuncExpr(fnoid, targettype,
+											 list_make1(expr),
+											 InvalidOid, InvalidOid,
+											 COERCE_EXPLICIT_CALL);
+
+			fexpr->location = location;
+
+			coerced = (Node *) fexpr;
+		}
+
+		if (coerced == orig)
+			expr = rawexpr;
+		else
+		{
+			ve = copyObject(ve);
+			ve->raw_expr = (Expr *) rawexpr;
+			ve->formatted_expr = (Expr *) coerced;
+
+			expr = (Node *) ve;
+		}
+	}
+
+	return expr;
+}
+
+/*
+ * Checks specified output format for its applicability to the target type.
+ */
+static void
+checkJsonOutputFormat(ParseState *pstate, const JsonFormat *format,
+					  Oid targettype, bool allow_format_for_non_strings)
+{
+	if (!allow_format_for_non_strings &&
+		format->format_type != JS_FORMAT_DEFAULT &&
+		(targettype != BYTEAOID &&
+		 targettype != JSONOID &&
+		 targettype != JSONBOID))
+	{
+		char		typcategory;
+		bool		typispreferred;
+
+		get_type_category_preferred(targettype, &typcategory, &typispreferred);
+
+		if (typcategory != TYPCATEGORY_STRING)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					parser_errposition(pstate, format->location),
+					errmsg("cannot use JSON format with non-string output types"));
+	}
+
+	if (format->format_type == JS_FORMAT_JSON)
+	{
+		JsonEncoding enc = format->encoding != JS_ENC_DEFAULT ?
+		format->encoding : JS_ENC_UTF8;
+
+		if (targettype != BYTEAOID &&
+			format->encoding != JS_ENC_DEFAULT)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					parser_errposition(pstate, format->location),
+					errmsg("cannot set JSON encoding for non-bytea output types"));
+
+		if (enc != JS_ENC_UTF8)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("unsupported JSON encoding"),
+					errhint("Only UTF8 JSON encoding is supported."),
+					parser_errposition(pstate, format->location));
+	}
+}
+
+/*
+ * Transform JSON output clause.
+ *
+ * Assigns target type oid and modifier.
+ * Assigns default format or checks specified format for its applicability to
+ * the target type.
+ */
+static JsonReturning *
+transformJsonOutput(ParseState *pstate, const JsonOutput *output,
+					bool allow_format)
+{
+	JsonReturning *ret;
+
+	/* if output clause is not specified, make default clause value */
+	if (!output)
+	{
+		ret = makeNode(JsonReturning);
+
+		ret->format = makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, -1);
+		ret->typid = InvalidOid;
+		ret->typmod = -1;
+
+		return ret;
+	}
+
+	ret = copyObject(output->returning);
+
+	typenameTypeIdAndMod(pstate, output->typeName, &ret->typid, &ret->typmod);
+
+	if (output->typeName->setof)
+		ereport(ERROR,
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("returning SETOF types is not supported in SQL/JSON functions"));
+
+	if (ret->format->format_type == JS_FORMAT_DEFAULT)
+		/* assign JSONB format when returning jsonb, or JSON format otherwise */
+		ret->format->format_type =
+			ret->typid == JSONBOID ? JS_FORMAT_JSONB : JS_FORMAT_JSON;
+	else
+		checkJsonOutputFormat(pstate, ret->format, ret->typid, allow_format);
+
+	return ret;
+}
+
+/*
+ * Transform JSON output clause of JSON constructor functions.
+ *
+ * Derive RETURNING type, if not specified, from argument types.
+ */
+static JsonReturning *
+transformJsonConstructorOutput(ParseState *pstate, JsonOutput *output,
+							   List *args)
+{
+	JsonReturning *returning = transformJsonOutput(pstate, output, true);
+
+	if (!OidIsValid(returning->typid))
+	{
+		ListCell   *lc;
+		bool		have_jsonb = false;
+
+		foreach(lc, args)
+		{
+			Node	   *expr = lfirst(lc);
+			Oid			typid = exprType(expr);
+
+			have_jsonb |= typid == JSONBOID;
+
+			if (have_jsonb)
+				break;
+		}
+
+		if (have_jsonb)
+		{
+			returning->typid = JSONBOID;
+			returning->format->format_type = JS_FORMAT_JSONB;
+		}
+		else
+		{
+			/* XXX TEXT is default by the standard, but we return JSON */
+			returning->typid = JSONOID;
+			returning->format->format_type = JS_FORMAT_JSON;
+		}
+
+		returning->typmod = -1;
+	}
+
+	return returning;
+}
+
+/*
+ * Coerce json[b]-valued function expression to the output type.
+ */
+static Node *
+coerceJsonFuncExpr(ParseState *pstate, Node *expr,
+				   const JsonReturning *returning, bool report_error)
+{
+	Node	   *res;
+	int			location;
+	Oid			exprtype = exprType(expr);
+
+	/* if output type is not specified or equals to function type, return */
+	if (!OidIsValid(returning->typid) || returning->typid == exprtype)
+		return expr;
+
+	location = exprLocation(expr);
+
+	if (location < 0)
+		location = returning->format->location;
+
+	/* special case for RETURNING bytea FORMAT json */
+	if (returning->format->format_type == JS_FORMAT_JSON &&
+		returning->typid == BYTEAOID)
+	{
+		/* encode json text into bytea using pg_convert_to() */
+		Node	   *texpr = coerce_to_specific_type(pstate, expr, TEXTOID,
+													"JSON_FUNCTION");
+		Const	   *enc = getJsonEncodingConst(returning->format);
+		FuncExpr   *fexpr = makeFuncExpr(F_CONVERT_TO, BYTEAOID,
+										 list_make2(texpr, enc),
+										 InvalidOid, InvalidOid,
+										 COERCE_EXPLICIT_CALL);
+
+		fexpr->location = location;
+
+		return (Node *) fexpr;
+	}
+
+	/* try to coerce expression to the output type */
+	res = coerce_to_target_type(pstate, expr, exprtype,
+								returning->typid, returning->typmod,
+	/* XXX throwing errors when casting to char(N) */
+								COERCION_EXPLICIT,
+								COERCE_EXPLICIT_CAST,
+								location);
+
+	if (!res && report_error)
+		ereport(ERROR,
+				errcode(ERRCODE_CANNOT_COERCE),
+				errmsg("cannot cast type %s to %s",
+					   format_type_be(exprtype),
+					   format_type_be(returning->typid)),
+				parser_coercion_errposition(pstate, location, expr));
+
+	return res;
+}
+
+static Node *
+makeJsonConstructorExpr(ParseState *pstate, JsonConstructorType type,
+						List *args, Expr *fexpr, JsonReturning *returning,
+						bool unique, bool absent_on_null, int location)
+{
+	JsonConstructorExpr *jsctor = makeNode(JsonConstructorExpr);
+	Node	   *placeholder;
+	Node	   *coercion;
+	Oid			intermediate_typid =
+	returning->format->format_type == JS_FORMAT_JSONB ? JSONBOID : JSONOID;
+
+	jsctor->args = args;
+	jsctor->func = fexpr;
+	jsctor->type = type;
+	jsctor->returning = returning;
+	jsctor->unique = unique;
+	jsctor->absent_on_null = absent_on_null;
+	jsctor->location = location;
+
+	if (fexpr)
+		placeholder = makeCaseTestExpr((Node *) fexpr);
+	else
+	{
+		CaseTestExpr *cte = makeNode(CaseTestExpr);
+
+		cte->typeId = intermediate_typid;
+		cte->typeMod = -1;
+		cte->collation = InvalidOid;
+
+		placeholder = (Node *) cte;
+	}
+
+	coercion = coerceJsonFuncExpr(pstate, placeholder, returning, true);
+
+	if (coercion != placeholder)
+		jsctor->coercion = (Expr *) coercion;
+
+	return (Node *) jsctor;
+}
+
+/*
+ * Transform JSON_OBJECT() constructor.
+ *
+ * JSON_OBJECT() is transformed into json[b]_build_object[_ext]() call
+ * depending on the output JSON format. The first two arguments of
+ * json[b]_build_object_ext() are absent_on_null and check_key_uniqueness.
+ *
+ * Then function call result is coerced to the target type.
+ */
+static Node *
+transformJsonObjectConstructor(ParseState *pstate, JsonObjectConstructor *ctor)
+{
+	JsonReturning *returning;
+	List	   *args = NIL;
+
+	/* transform key-value pairs, if any */
+	if (ctor->exprs)
+	{
+		ListCell   *lc;
+
+		/* transform and append key-value arguments */
+		foreach(lc, ctor->exprs)
+		{
+			JsonKeyValue *kv = castNode(JsonKeyValue, lfirst(lc));
+			Node	   *key = transformExprRecurse(pstate, (Node *) kv->key);
+			Node	   *val = transformJsonValueExpr(pstate, kv->value,
+													 JS_FORMAT_DEFAULT);
+
+			args = lappend(args, key);
+			args = lappend(args, val);
+		}
+	}
+
+	returning = transformJsonConstructorOutput(pstate, ctor->output, args);
+
+	return makeJsonConstructorExpr(pstate, JSCTOR_JSON_OBJECT, args, NULL,
+								   returning, ctor->unique,
+								   ctor->absent_on_null, ctor->location);
+}
+
+/*
+ * Transform JSON_ARRAY(query [FORMAT] [RETURNING] [ON NULL]) into
+ *  (SELECT  JSON_ARRAYAGG(a  [FORMAT] [RETURNING] [ON NULL]) FROM (query) q(a))
+ */
+static Node *
+transformJsonArrayQueryConstructor(ParseState *pstate,
+								   JsonArrayQueryConstructor *ctor)
+{
+	SubLink    *sublink = makeNode(SubLink);
+	SelectStmt *select = makeNode(SelectStmt);
+	RangeSubselect *range = makeNode(RangeSubselect);
+	Alias	   *alias = makeNode(Alias);
+	ResTarget  *target = makeNode(ResTarget);
+	JsonArrayAgg *agg = makeNode(JsonArrayAgg);
+	ColumnRef  *colref = makeNode(ColumnRef);
+	Query	   *query;
+	ParseState *qpstate;
+
+	/* Transform query only for counting target list entries. */
+	qpstate = make_parsestate(pstate);
+
+	query = transformStmt(qpstate, ctor->query);
+
+	if (count_nonjunk_tlist_entries(query->targetList) != 1)
+		ereport(ERROR,
+				errcode(ERRCODE_SYNTAX_ERROR),
+				errmsg("subquery must return only one column"),
+				parser_errposition(pstate, ctor->location));
+
+	free_parsestate(qpstate);
+
+	colref->fields = list_make2(makeString(pstrdup("q")),
+								makeString(pstrdup("a")));
+	colref->location = ctor->location;
+
+	agg->arg = makeJsonValueExpr((Expr *) colref, ctor->format);
+	agg->absent_on_null = ctor->absent_on_null;
+	agg->constructor = makeNode(JsonAggConstructor);
+	agg->constructor->agg_order = NIL;
+	agg->constructor->output = ctor->output;
+	agg->constructor->location = ctor->location;
+
+	target->name = NULL;
+	target->indirection = NIL;
+	target->val = (Node *) agg;
+	target->location = ctor->location;
+
+	alias->aliasname = pstrdup("q");
+	alias->colnames = list_make1(makeString(pstrdup("a")));
+
+	range->lateral = false;
+	range->subquery = ctor->query;
+	range->alias = alias;
+
+	select->targetList = list_make1(target);
+	select->fromClause = list_make1(range);
+
+	sublink->subLinkType = EXPR_SUBLINK;
+	sublink->subLinkId = 0;
+	sublink->testexpr = NULL;
+	sublink->operName = NIL;
+	sublink->subselect = (Node *) select;
+	sublink->location = ctor->location;
+
+	return transformExprRecurse(pstate, (Node *) sublink);
+}
+
+/*
+ * Common code for JSON_OBJECTAGG and JSON_ARRAYAGG transformation.
+ */
+static Node *
+transformJsonAggConstructor(ParseState *pstate, JsonAggConstructor *agg_ctor,
+							JsonReturning *returning, List *args,
+							const char *aggfn, Oid aggtype,
+							JsonConstructorType ctor_type,
+							bool unique, bool absent_on_null)
+{
+	Oid			aggfnoid;
+	Node	   *node;
+	Expr	   *aggfilter = agg_ctor->agg_filter ? (Expr *)
+	transformWhereClause(pstate, agg_ctor->agg_filter,
+						 EXPR_KIND_FILTER, "FILTER") : NULL;
+
+	aggfnoid = DatumGetInt32(DirectFunctionCall1(regprocin,
+												 CStringGetDatum(aggfn)));
+
+	if (agg_ctor->over)
+	{
+		/* window function */
+		WindowFunc *wfunc = makeNode(WindowFunc);
+
+		wfunc->winfnoid = aggfnoid;
+		wfunc->wintype = aggtype;
+		/* wincollid and inputcollid will be set by parse_collate.c */
+		wfunc->args = args;
+		/* winref will be set by transformWindowFuncCall */
+		wfunc->winstar = false;
+		wfunc->winagg = true;
+		wfunc->aggfilter = aggfilter;
+		wfunc->location = agg_ctor->location;
+
+		/*
+		 * ordered aggs not allowed in windows yet
+		 */
+		if (agg_ctor->agg_order != NIL)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("aggregate ORDER BY is not implemented for window functions"),
+					parser_errposition(pstate, agg_ctor->location));
+
+		/* parse_agg.c does additional window-func-specific processing */
+		transformWindowFuncCall(pstate, wfunc, agg_ctor->over);
+
+		node = (Node *) wfunc;
+	}
+	else
+	{
+		Aggref	   *aggref = makeNode(Aggref);
+
+		aggref->aggfnoid = aggfnoid;
+		aggref->aggtype = aggtype;
+
+		/* aggcollid and inputcollid will be set by parse_collate.c */
+		aggref->aggtranstype = InvalidOid;	/* will be set by planner */
+		/* aggargtypes will be set by transformAggregateCall */
+		/* aggdirectargs and args will be set by transformAggregateCall */
+		/* aggorder and aggdistinct will be set by transformAggregateCall */
+		aggref->aggfilter = aggfilter;
+		aggref->aggstar = false;
+		aggref->aggvariadic = false;
+		aggref->aggkind = AGGKIND_NORMAL;
+		/* agglevelsup will be set by transformAggregateCall */
+		aggref->aggsplit = AGGSPLIT_SIMPLE; /* planner might change this */
+		aggref->location = agg_ctor->location;
+
+		transformAggregateCall(pstate, aggref, args, agg_ctor->agg_order, false);
+
+		node = (Node *) aggref;
+	}
+
+	return makeJsonConstructorExpr(pstate, ctor_type, NIL, (Expr *) node,
+								   returning, unique, absent_on_null,
+								   agg_ctor->location);
+}
+
+/*
+ * Transform JSON_OBJECTAGG() aggregate function.
+ *
+ * JSON_OBJECTAGG() is transformed into
+ * json[b]_objectagg(key, value, absent_on_null, check_unique) call depending on
+ * the output JSON format.  Then the function call result is coerced to the
+ * target output type.
+ */
+static Node *
+transformJsonObjectAgg(ParseState *pstate, JsonObjectAgg *agg)
+{
+	JsonReturning *returning;
+	Node	   *key;
+	Node	   *val;
+	List	   *args;
+	const char *aggfnname;
+	Oid			aggtype;
+
+	key = transformExprRecurse(pstate, (Node *) agg->arg->key);
+	val = transformJsonValueExpr(pstate, agg->arg->value, JS_FORMAT_DEFAULT);
+	args = list_make2(key, val);
+
+	returning = transformJsonConstructorOutput(pstate, agg->constructor->output,
+											   args);
+
+	if (returning->format->format_type == JS_FORMAT_JSONB)
+	{
+		if (agg->absent_on_null)
+			if (agg->unique)
+				aggfnname = "pg_catalog.jsonb_object_agg_unique_strict";
+			else
+				aggfnname = "pg_catalog.jsonb_object_agg_strict";
+		else if (agg->unique)
+			aggfnname = "pg_catalog.jsonb_object_agg_unique";
+		else
+			aggfnname = "pg_catalog.jsonb_object_agg";
+
+		aggtype = JSONBOID;
+	}
+	else
+	{
+		if (agg->absent_on_null)
+			if (agg->unique)
+				aggfnname = "pg_catalog.json_object_agg_unique_strict";
+			else
+				aggfnname = "pg_catalog.json_object_agg_strict";
+		else if (agg->unique)
+			aggfnname = "pg_catalog.json_object_agg_unique";
+		else
+			aggfnname = "pg_catalog.json_object_agg";
+
+		aggtype = JSONOID;
+	}
+
+	return transformJsonAggConstructor(pstate, agg->constructor, returning,
+									   args, aggfnname, aggtype,
+									   JSCTOR_JSON_OBJECTAGG,
+									   agg->unique, agg->absent_on_null);
+}
+
+/*
+ * Transform JSON_ARRAYAGG() aggregate function.
+ *
+ * JSON_ARRAYAGG() is transformed into json[b]_agg[_strict]() call depending
+ * on the output JSON format and absent_on_null.  Then the function call result
+ * is coerced to the target output type.
+ */
+static Node *
+transformJsonArrayAgg(ParseState *pstate, JsonArrayAgg *agg)
+{
+	JsonReturning *returning;
+	Node	   *arg;
+	const char *aggfnname;
+	Oid			aggtype;
+
+	arg = transformJsonValueExpr(pstate, agg->arg, JS_FORMAT_DEFAULT);
+
+	returning = transformJsonConstructorOutput(pstate, agg->constructor->output,
+											   list_make1(arg));
+
+	if (returning->format->format_type == JS_FORMAT_JSONB)
+	{
+		aggfnname = agg->absent_on_null ?
+			"pg_catalog.jsonb_agg_strict" : "pg_catalog.jsonb_agg";
+		aggtype = JSONBOID;
+	}
+	else
+	{
+		aggfnname = agg->absent_on_null ?
+			"pg_catalog.json_agg_strict" : "pg_catalog.json_agg";
+		aggtype = JSONOID;
+	}
+
+	return transformJsonAggConstructor(pstate, agg->constructor, returning,
+									   list_make1(arg), aggfnname, aggtype,
+									   JSCTOR_JSON_ARRAYAGG,
+									   false, agg->absent_on_null);
+}
+
+/*
+ * Transform JSON_ARRAY() constructor.
+ *
+ * JSON_ARRAY() is transformed into json[b]_build_array[_ext]() call
+ * depending on the output JSON format. The first argument of
+ * json[b]_build_array_ext() is absent_on_null.
+ *
+ * Then function call result is coerced to the target type.
+ */
+static Node *
+transformJsonArrayConstructor(ParseState *pstate, JsonArrayConstructor *ctor)
+{
+	JsonReturning *returning;
+	List	   *args = NIL;
+
+	/* transform element expressions, if any */
+	if (ctor->exprs)
+	{
+		ListCell   *lc;
+
+		/* transform and append element arguments */
+		foreach(lc, ctor->exprs)
+		{
+			JsonValueExpr *jsval = castNode(JsonValueExpr, lfirst(lc));
+			Node	   *val = transformJsonValueExpr(pstate, jsval,
+													 JS_FORMAT_DEFAULT);
+
+			args = lappend(args, val);
+		}
+	}
+
+	returning = transformJsonConstructorOutput(pstate, ctor->output, args);
+
+	return makeJsonConstructorExpr(pstate, JSCTOR_JSON_ARRAY, args, NULL,
+								   returning, false, ctor->absent_on_null,
+								   ctor->location);
+}
diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
index 25781db5c1d..e77b542fd76 100644
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@@ -1907,8 +1907,26 @@ FigureColnameInternal(Node *node, char **name)
 			}
 			break;
 		case T_XmlSerialize:
+			/* make XMLSERIALIZE act like a regular function */
 			*name = "xmlserialize";
 			return 2;
+		case T_JsonObjectConstructor:
+			/* make JSON_OBJECT act like a regular function */
+			*name = "json_object";
+			return 2;
+		case T_JsonArrayConstructor:
+		case T_JsonArrayQueryConstructor:
+			/* make JSON_ARRAY act like a regular function */
+			*name = "json_array";
+			return 2;
+		case T_JsonObjectAgg:
+			/* make JSON_OBJECTAGG act like a regular function */
+			*name = "json_objectagg";
+			return 2;
+		case T_JsonArrayAgg:
+			/* make JSON_ARRAYAGG act like a regular function */
+			*name = "json_arrayagg";
+			return 2;
 		default:
 			break;
 	}
diff --git a/src/backend/parser/parser.c b/src/backend/parser/parser.c
index aa4dce6ee9c..65eb0876575 100644
--- a/src/backend/parser/parser.c
+++ b/src/backend/parser/parser.c
@@ -137,6 +137,9 @@ base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
 	 */
 	switch (cur_token)
 	{
+		case FORMAT:
+			cur_token_length = 6;
+			break;
 		case NOT:
 			cur_token_length = 3;
 			break;
@@ -150,6 +153,9 @@ base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
 		case USCONST:
 			cur_token_length = strlen(yyextra->core_yy_extra.scanbuf + *llocp);
 			break;
+		case WITHOUT:
+			cur_token_length = 7;
+			break;
 		default:
 			return cur_token;
 	}
@@ -188,6 +194,16 @@ base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
 	/* Replace cur_token if needed, based on lookahead */
 	switch (cur_token)
 	{
+		case FORMAT:
+			/* Replace FORMAT by FORMAT_LA if it's followed by JSON */
+			switch (next_token)
+			{
+				case JSON:
+					cur_token = FORMAT_LA;
+					break;
+			}
+			break;
+
 		case NOT:
 			/* Replace NOT by NOT_LA if it's followed by BETWEEN, IN, etc */
 			switch (next_token)
@@ -224,6 +240,16 @@ base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
 			}
 			break;
 
+		case WITHOUT:
+			/* Replace WITHOUT by WITHOUT_LA if it's followed by UNIQUE */
+			switch (next_token)
+			{
+				case UNIQUE:
+					cur_token = WITHOUT_LA;
+					break;
+			}
+			break;
+
 		case UIDENT:
 		case USCONST:
 			/* Look ahead for UESCAPE */
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 06d8bea9cde..dcd2bb2234a 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -13,7 +13,9 @@
  */
 #include "postgres.h"
 
+#include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
+#include "common/hashfn.h"
 #include "funcapi.h"
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
@@ -42,6 +44,34 @@ typedef enum					/* type categories for datum_to_json */
 	JSONTYPE_OTHER				/* all else */
 } JsonTypeCategory;
 
+
+/*
+ * Support for fast key uniqueness checking.
+ *
+ * We maintain a hash table of used keys in JSON objects for fast detection
+ * of duplicates.
+ */
+/* Common context for key uniqueness check */
+typedef struct HTAB *JsonUniqueCheckState;	/* hash table for key names */
+
+/* Hash entry for JsonUniqueCheckState */
+typedef struct JsonUniqueHashEntry
+{
+	const char *key;
+	int			key_len;
+	int			object_id;
+} JsonUniqueHashEntry;
+
+/* Context struct for key uniqueness check during JSON building */
+typedef struct JsonUniqueBuilderState
+{
+	JsonUniqueCheckState check; /* unique check */
+	StringInfoData skipped_keys;	/* skipped keys with NULL values */
+	MemoryContext mcxt;			/* context for saving skipped keys */
+} JsonUniqueBuilderState;
+
+
+/* State struct for JSON aggregation */
 typedef struct JsonAggState
 {
 	StringInfo	str;
@@ -49,6 +79,7 @@ typedef struct JsonAggState
 	Oid			key_output_func;
 	JsonTypeCategory val_category;
 	Oid			val_output_func;
+	JsonUniqueBuilderState unique_check;
 } JsonAggState;
 
 static void composite_to_json(Datum composite, StringInfo result,
@@ -724,6 +755,48 @@ row_to_json_pretty(PG_FUNCTION_ARGS)
 }
 
 /*
+ * Is the given type immutable when coming out of a JSON context?
+ *
+ * At present, datetimes are all considered mutable, because they
+ * depend on timezone.  XXX we should also drill down into objects
+ * and arrays, but do not.
+ */
+bool
+to_json_is_immutable(Oid typoid)
+{
+	JsonTypeCategory tcategory;
+	Oid			outfuncoid;
+
+	json_categorize_type(typoid, &tcategory, &outfuncoid);
+
+	switch (tcategory)
+	{
+		case JSONTYPE_BOOL:
+		case JSONTYPE_JSON:
+		case JSONTYPE_NULL:
+			return true;
+
+		case JSONTYPE_DATE:
+		case JSONTYPE_TIMESTAMP:
+		case JSONTYPE_TIMESTAMPTZ:
+			return false;
+
+		case JSONTYPE_ARRAY:
+			return false;		/* TODO recurse into elements */
+
+		case JSONTYPE_COMPOSITE:
+			return false;		/* TODO recurse into fields */
+
+		case JSONTYPE_NUMERIC:
+		case JSONTYPE_CAST:
+		case JSONTYPE_OTHER:
+			return func_volatile(outfuncoid) == PROVOLATILE_IMMUTABLE;
+	}
+
+	return false;				/* not reached */
+}
+
+/*
  * SQL function to_json(anyvalue)
  */
 Datum
@@ -755,8 +828,8 @@ to_json(PG_FUNCTION_ARGS)
  *
  * aggregate input column as a json array value.
  */
-Datum
-json_agg_transfn(PG_FUNCTION_ARGS)
+static Datum
+json_agg_transfn_worker(FunctionCallInfo fcinfo, bool absent_on_null)
 {
 	MemoryContext aggcontext,
 				oldcontext;
@@ -796,9 +869,14 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	else
 	{
 		state = (JsonAggState *) PG_GETARG_POINTER(0);
-		appendStringInfoString(state->str, ", ");
 	}
 
+	if (absent_on_null && PG_ARGISNULL(1))
+		PG_RETURN_POINTER(state);
+
+	if (state->str->len > 1)
+		appendStringInfoString(state->str, ", ");
+
 	/* fast path for NULLs */
 	if (PG_ARGISNULL(1))
 	{
@@ -810,7 +888,7 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	val = PG_GETARG_DATUM(1);
 
 	/* add some whitespace if structured type and not first item */
-	if (!PG_ARGISNULL(0) &&
+	if (!PG_ARGISNULL(0) && state->str->len > 1 &&
 		(state->val_category == JSONTYPE_ARRAY ||
 		 state->val_category == JSONTYPE_COMPOSITE))
 	{
@@ -828,6 +906,25 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+
+/*
+ * json_agg aggregate function
+ */
+Datum
+json_agg_transfn(PG_FUNCTION_ARGS)
+{
+	return json_agg_transfn_worker(fcinfo, false);
+}
+
+/*
+ * json_agg_strict aggregate function
+ */
+Datum
+json_agg_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return json_agg_transfn_worker(fcinfo, true);
+}
+
 /*
  * json_agg final function
  */
@@ -851,18 +948,120 @@ json_agg_finalfn(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(catenate_stringinfo_string(state->str, "]"));
 }
 
+/* Functions implementing hash table for key uniqueness check */
+static uint32
+json_unique_hash(const void *key, Size keysize)
+{
+	const JsonUniqueHashEntry *entry = (JsonUniqueHashEntry *) key;
+	uint32		hash = hash_bytes_uint32(entry->object_id);
+
+	hash ^= hash_bytes((const unsigned char *) entry->key, entry->key_len);
+
+	return DatumGetUInt32(hash);
+}
+
+static int
+json_unique_hash_match(const void *key1, const void *key2, Size keysize)
+{
+	const JsonUniqueHashEntry *entry1 = (const JsonUniqueHashEntry *) key1;
+	const JsonUniqueHashEntry *entry2 = (const JsonUniqueHashEntry *) key2;
+
+	if (entry1->object_id != entry2->object_id)
+		return entry1->object_id > entry2->object_id ? 1 : -1;
+
+	if (entry1->key_len != entry2->key_len)
+		return entry1->key_len > entry2->key_len ? 1 : -1;
+
+	return strncmp(entry1->key, entry2->key, entry1->key_len);
+}
+
+/*
+ * Uniqueness detection support.
+ *
+ * In order to detect uniqueness during building or parsing of a JSON
+ * object, we maintain a hash table of key names already seen.
+ */
+static void
+json_unique_check_init(JsonUniqueCheckState *cxt)
+{
+	HASHCTL		ctl;
+
+	memset(&ctl, 0, sizeof(ctl));
+	ctl.keysize = sizeof(JsonUniqueHashEntry);
+	ctl.entrysize = sizeof(JsonUniqueHashEntry);
+	ctl.hcxt = CurrentMemoryContext;
+	ctl.hash = json_unique_hash;
+	ctl.match = json_unique_hash_match;
+
+	*cxt = hash_create("json object hashtable",
+					   32,
+					   &ctl,
+					   HASH_ELEM | HASH_CONTEXT | HASH_FUNCTION | HASH_COMPARE);
+}
+
+static void
+json_unique_builder_init(JsonUniqueBuilderState *cxt)
+{
+	json_unique_check_init(&cxt->check);
+	cxt->mcxt = CurrentMemoryContext;
+	cxt->skipped_keys.data = NULL;
+}
+
+static bool
+json_unique_check_key(JsonUniqueCheckState *cxt, const char *key, int object_id)
+{
+	JsonUniqueHashEntry entry;
+	bool		found;
+
+	entry.key = key;
+	entry.key_len = strlen(key);
+	entry.object_id = object_id;
+
+	(void) hash_search(*cxt, &entry, HASH_ENTER, &found);
+
+	return !found;
+}
+
+/*
+ * On-demand initialization of a throwaway StringInfo.  This is used to
+ * read a key name that we don't need to store in the output object, for
+ * duplicate key detection when the value is NULL.
+ */
+static StringInfo
+json_unique_builder_get_throwawaybuf(JsonUniqueBuilderState *cxt)
+{
+	StringInfo	out = &cxt->skipped_keys;
+
+	if (!out->data)
+	{
+		MemoryContext oldcxt = MemoryContextSwitchTo(cxt->mcxt);
+
+		initStringInfo(out);
+		MemoryContextSwitchTo(oldcxt);
+	}
+	else
+		/* Just reset the string to empty */
+		out->len = 0;
+
+	return out;
+}
+
 /*
  * json_object_agg transition function.
  *
  * aggregate two input columns as a single json object value.
  */
-Datum
-json_object_agg_transfn(PG_FUNCTION_ARGS)
+static Datum
+json_object_agg_transfn_worker(FunctionCallInfo fcinfo,
+							   bool absent_on_null, bool unique_keys)
 {
 	MemoryContext aggcontext,
 				oldcontext;
 	JsonAggState *state;
+	StringInfo	out;
 	Datum		arg;
+	bool		skip;
+	int			key_offset;
 
 	if (!AggCheckCallContext(fcinfo, &aggcontext))
 	{
@@ -877,12 +1076,16 @@ json_object_agg_transfn(PG_FUNCTION_ARGS)
 		/*
 		 * Make the StringInfo in a context where it will persist for the
 		 * duration of the aggregate call. Switching context is only needed
-		 * for this initial step, as the StringInfo routines make sure they
-		 * use the right context to enlarge the object if necessary.
+		 * for this initial step, as the StringInfo and dynahash routines make
+		 * sure they use the right context to enlarge the object if necessary.
 		 */
 		oldcontext = MemoryContextSwitchTo(aggcontext);
 		state = (JsonAggState *) palloc(sizeof(JsonAggState));
 		state->str = makeStringInfo();
+		if (unique_keys)
+			json_unique_builder_init(&state->unique_check);
+		else
+			memset(&state->unique_check, 0, sizeof(state->unique_check));
 		MemoryContextSwitchTo(oldcontext);
 
 		arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);
@@ -910,7 +1113,6 @@ json_object_agg_transfn(PG_FUNCTION_ARGS)
 	else
 	{
 		state = (JsonAggState *) PG_GETARG_POINTER(0);
-		appendStringInfoString(state->str, ", ");
 	}
 
 	/*
@@ -923,14 +1125,56 @@ json_object_agg_transfn(PG_FUNCTION_ARGS)
 
 	if (PG_ARGISNULL(1))
 		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("field name must not be null")));
+				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+				 errmsg("null value not allowed for object key")));
+
+	/* Skip null values if absent_on_null */
+	skip = absent_on_null && PG_ARGISNULL(2);
+
+	if (skip)
+	{
+		/*
+		 * We got a NULL value and we're not storing those; if we're not
+		 * testing key uniqueness, we're done.  If we are, use the throwaway
+		 * buffer to store the key name so that we can check it.
+		 */
+		if (!unique_keys)
+			PG_RETURN_POINTER(state);
+
+		out = json_unique_builder_get_throwawaybuf(&state->unique_check);
+	}
+	else
+	{
+		out = state->str;
+
+		/*
+		 * Append comma delimiter only if we have already output some fields
+		 * after the initial string "{ ".
+		 */
+		if (out->len > 2)
+			appendStringInfoString(out, ", ");
+	}
 
 	arg = PG_GETARG_DATUM(1);
 
-	datum_to_json(arg, false, state->str, state->key_category,
+	key_offset = out->len;
+
+	datum_to_json(arg, false, out, state->key_category,
 				  state->key_output_func, true);
 
+	if (unique_keys)
+	{
+		const char *key = &out->data[key_offset];
+
+		if (!json_unique_check_key(&state->unique_check.check, key, 0))
+			ereport(ERROR,
+					errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
+					errmsg("duplicate JSON key %s", key));
+
+		if (skip)
+			PG_RETURN_POINTER(state);
+	}
+
 	appendStringInfoString(state->str, " : ");
 
 	if (PG_ARGISNULL(2))
@@ -945,6 +1189,42 @@ json_object_agg_transfn(PG_FUNCTION_ARGS)
 }
 
 /*
+ * json_object_agg aggregate function
+ */
+Datum
+json_object_agg_transfn(PG_FUNCTION_ARGS)
+{
+	return json_object_agg_transfn_worker(fcinfo, false, false);
+}
+
+/*
+ * json_object_agg_strict aggregate function
+ */
+Datum
+json_object_agg_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return json_object_agg_transfn_worker(fcinfo, true, false);
+}
+
+/*
+ * json_object_agg_unique aggregate function
+ */
+Datum
+json_object_agg_unique_transfn(PG_FUNCTION_ARGS)
+{
+	return json_object_agg_transfn_worker(fcinfo, false, true);
+}
+
+/*
+ * json_object_agg_unique_strict aggregate function
+ */
+Datum
+json_object_agg_unique_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return json_object_agg_transfn_worker(fcinfo, true, true);
+}
+
+/*
  * json_object_agg final function.
  */
 Datum
@@ -985,25 +1265,14 @@ catenate_stringinfo_string(StringInfo buffer, const char *addon)
 	return result;
 }
 
-/*
- * SQL function json_build_object(variadic "any")
- */
 Datum
-json_build_object(PG_FUNCTION_ARGS)
+json_build_object_worker(int nargs, Datum *args, bool *nulls, Oid *types,
+						 bool absent_on_null, bool unique_keys)
 {
-	int			nargs;
 	int			i;
 	const char *sep = "";
 	StringInfo	result;
-	Datum	   *args;
-	bool	   *nulls;
-	Oid		   *types;
-
-	/* fetch argument values to build the object */
-	nargs = extract_variadic_args(fcinfo, 0, false, &args, &types, &nulls);
-
-	if (nargs < 0)
-		PG_RETURN_NULL();
+	JsonUniqueBuilderState unique_check;
 
 	if (nargs % 2 != 0)
 		ereport(ERROR,
@@ -1017,19 +1286,57 @@ json_build_object(PG_FUNCTION_ARGS)
 
 	appendStringInfoChar(result, '{');
 
+	if (unique_keys)
+		json_unique_builder_init(&unique_check);
+
 	for (i = 0; i < nargs; i += 2)
 	{
-		appendStringInfoString(result, sep);
-		sep = ", ";
+		StringInfo	out;
+		bool		skip;
+		int			key_offset;
+
+		/* Skip null values if absent_on_null */
+		skip = absent_on_null && nulls[i + 1];
+
+		if (skip)
+		{
+			/* If key uniqueness check is needed we must save skipped keys */
+			if (!unique_keys)
+				continue;
+
+			out = json_unique_builder_get_throwawaybuf(&unique_check);
+		}
+		else
+		{
+			appendStringInfoString(result, sep);
+			sep = ", ";
+			out = result;
+		}
 
 		/* process key */
 		if (nulls[i])
 			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("argument %d cannot be null", i + 1),
-					 errhint("Object keys should be text.")));
+					(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+					 errmsg("null value not allowed for object key")));
+
+		/* save key offset before appending it */
+		key_offset = out->len;
 
-		add_json(args[i], false, result, types[i], true);
+		add_json(args[i], false, out, types[i], true);
+
+		if (unique_keys)
+		{
+			/* check key uniqueness after key appending */
+			const char *key = &out->data[key_offset];
+
+			if (!json_unique_check_key(&unique_check.check, key, 0))
+				ereport(ERROR,
+						errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
+						errmsg("duplicate JSON key %s", key));
+
+			if (skip)
+				continue;
+		}
 
 		appendStringInfoString(result, " : ");
 
@@ -1039,7 +1346,27 @@ json_build_object(PG_FUNCTION_ARGS)
 
 	appendStringInfoChar(result, '}');
 
-	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
+	return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
+}
+
+/*
+ * SQL function json_build_object(variadic "any")
+ */
+Datum
+json_build_object(PG_FUNCTION_ARGS)
+{
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the object */
+	int			nargs = extract_variadic_args(fcinfo, 0, true,
+											  &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_DATUM(json_build_object_worker(nargs, args, nulls, types, false, false));
 }
 
 /*
@@ -1051,25 +1378,13 @@ json_build_object_noargs(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(cstring_to_text_with_len("{}", 2));
 }
 
-/*
- * SQL function json_build_array(variadic "any")
- */
 Datum
-json_build_array(PG_FUNCTION_ARGS)
+json_build_array_worker(int nargs, Datum *args, bool *nulls, Oid *types,
+						bool absent_on_null)
 {
-	int			nargs;
 	int			i;
 	const char *sep = "";
 	StringInfo	result;
-	Datum	   *args;
-	bool	   *nulls;
-	Oid		   *types;
-
-	/* fetch argument values to build the array */
-	nargs = extract_variadic_args(fcinfo, 0, false, &args, &types, &nulls);
-
-	if (nargs < 0)
-		PG_RETURN_NULL();
 
 	result = makeStringInfo();
 
@@ -1077,6 +1392,9 @@ json_build_array(PG_FUNCTION_ARGS)
 
 	for (i = 0; i < nargs; i++)
 	{
+		if (absent_on_null && nulls[i])
+			continue;
+
 		appendStringInfoString(result, sep);
 		sep = ", ";
 		add_json(args[i], nulls[i], result, types[i], false);
@@ -1084,7 +1402,27 @@ json_build_array(PG_FUNCTION_ARGS)
 
 	appendStringInfoChar(result, ']');
 
-	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
+	return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
+}
+
+/*
+ * SQL function json_build_array(variadic "any")
+ */
+Datum
+json_build_array(PG_FUNCTION_ARGS)
+{
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the object */
+	int			nargs = extract_variadic_args(fcinfo, 0, true,
+											  &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_DATUM(json_build_array_worker(nargs, args, nulls, types, false));
 }
 
 /*
diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
index 0539f41c172..cf43c3f2ded 100644
--- a/src/backend/utils/adt/jsonb.c
+++ b/src/backend/utils/adt/jsonb.c
@@ -14,6 +14,7 @@
 
 #include "access/htup_details.h"
 #include "access/transam.h"
+#include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "libpq/pqformat.h"
@@ -1150,6 +1151,49 @@ add_jsonb(Datum val, bool is_null, JsonbInState *result,
 }
 
 /*
+ * Is the given type immutable when coming out of a JSONB context?
+ *
+ * At present, datetimes are all considered mutable, because they
+ * depend on timezone.  XXX we should also drill down into objects and
+ * arrays, but do not.
+ */
+bool
+to_jsonb_is_immutable(Oid typoid)
+{
+	JsonbTypeCategory tcategory;
+	Oid			outfuncoid;
+
+	jsonb_categorize_type(typoid, &tcategory, &outfuncoid);
+
+	switch (tcategory)
+	{
+		case JSONBTYPE_NULL:
+		case JSONBTYPE_BOOL:
+		case JSONBTYPE_JSON:
+		case JSONBTYPE_JSONB:
+			return true;
+
+		case JSONBTYPE_DATE:
+		case JSONBTYPE_TIMESTAMP:
+		case JSONBTYPE_TIMESTAMPTZ:
+			return false;
+
+		case JSONBTYPE_ARRAY:
+			return false;		/* TODO recurse into elements */
+
+		case JSONBTYPE_COMPOSITE:
+			return false;		/* TODO recurse into fields */
+
+		case JSONBTYPE_NUMERIC:
+		case JSONBTYPE_JSONCAST:
+		case JSONBTYPE_OTHER:
+			return func_volatile(outfuncoid) == PROVOLATILE_IMMUTABLE;
+	}
+
+	return false;				/* not reached */
+}
+
+/*
  * SQL function to_jsonb(anyvalue)
  */
 Datum
@@ -1176,24 +1220,12 @@ to_jsonb(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
 }
 
-/*
- * SQL function jsonb_build_object(variadic "any")
- */
 Datum
-jsonb_build_object(PG_FUNCTION_ARGS)
+jsonb_build_object_worker(int nargs, Datum *args, bool *nulls, Oid *types,
+						  bool absent_on_null, bool unique_keys)
 {
-	int			nargs;
 	int			i;
 	JsonbInState result;
-	Datum	   *args;
-	bool	   *nulls;
-	Oid		   *types;
-
-	/* build argument values to build the object */
-	nargs = extract_variadic_args(fcinfo, 0, true, &args, &types, &nulls);
-
-	if (nargs < 0)
-		PG_RETURN_NULL();
 
 	if (nargs % 2 != 0)
 		ereport(ERROR,
@@ -1206,15 +1238,26 @@ jsonb_build_object(PG_FUNCTION_ARGS)
 	memset(&result, 0, sizeof(JsonbInState));
 
 	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
+	result.parseState->unique_keys = unique_keys;
+	result.parseState->skip_nulls = absent_on_null;
 
 	for (i = 0; i < nargs; i += 2)
 	{
 		/* process key */
+		bool		skip;
+
 		if (nulls[i])
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("argument %d: key must not be null", i + 1)));
 
+		/* skip null values if absent_on_null */
+		skip = absent_on_null && nulls[i + 1];
+
+		/* we need to save skipped keys for the key uniqueness check */
+		if (skip && !unique_keys)
+			continue;
+
 		add_jsonb(args[i], false, &result, types[i], true);
 
 		/* process value */
@@ -1223,7 +1266,27 @@ jsonb_build_object(PG_FUNCTION_ARGS)
 
 	result.res = pushJsonbValue(&result.parseState, WJB_END_OBJECT, NULL);
 
-	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
+	return JsonbPGetDatum(JsonbValueToJsonb(result.res));
+}
+
+/*
+ * SQL function jsonb_build_object(variadic "any")
+ */
+Datum
+jsonb_build_object(PG_FUNCTION_ARGS)
+{
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the object */
+	int			nargs = extract_variadic_args(fcinfo, 0, true,
+											  &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_DATUM(jsonb_build_object_worker(nargs, args, nulls, types, false, false));
 }
 
 /*
@@ -1242,38 +1305,52 @@ jsonb_build_object_noargs(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
 }
 
-/*
- * SQL function jsonb_build_array(variadic "any")
- */
 Datum
-jsonb_build_array(PG_FUNCTION_ARGS)
+jsonb_build_array_worker(int nargs, Datum *args, bool *nulls, Oid *types,
+						 bool absent_on_null)
 {
-	int			nargs;
 	int			i;
 	JsonbInState result;
-	Datum	   *args;
-	bool	   *nulls;
-	Oid		   *types;
-
-	/* build argument values to build the array */
-	nargs = extract_variadic_args(fcinfo, 0, true, &args, &types, &nulls);
-
-	if (nargs < 0)
-		PG_RETURN_NULL();
 
 	memset(&result, 0, sizeof(JsonbInState));
 
 	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_ARRAY, NULL);
 
 	for (i = 0; i < nargs; i++)
+	{
+		if (absent_on_null && nulls[i])
+			continue;
+
 		add_jsonb(args[i], nulls[i], &result, types[i], false);
+	}
 
 	result.res = pushJsonbValue(&result.parseState, WJB_END_ARRAY, NULL);
 
-	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
+	return JsonbPGetDatum(JsonbValueToJsonb(result.res));
 }
 
 /*
+ * SQL function jsonb_build_array(variadic "any")
+ */
+Datum
+jsonb_build_array(PG_FUNCTION_ARGS)
+{
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the object */
+	int			nargs = extract_variadic_args(fcinfo, 0, true,
+											  &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_DATUM(jsonb_build_array_worker(nargs, args, nulls, types, false));
+}
+
+
+/*
  * degenerate case of jsonb_build_array where it gets 0 arguments.
  */
 Datum
@@ -1506,6 +1583,8 @@ clone_parse_state(JsonbParseState *state)
 	{
 		ocursor->contVal = icursor->contVal;
 		ocursor->size = icursor->size;
+		ocursor->unique_keys = icursor->unique_keys;
+		ocursor->skip_nulls = icursor->skip_nulls;
 		icursor = icursor->next;
 		if (icursor == NULL)
 			break;
@@ -1517,12 +1596,8 @@ clone_parse_state(JsonbParseState *state)
 	return result;
 }
 
-
-/*
- * jsonb_agg aggregate function
- */
-Datum
-jsonb_agg_transfn(PG_FUNCTION_ARGS)
+static Datum
+jsonb_agg_transfn_worker(FunctionCallInfo fcinfo, bool absent_on_null)
 {
 	MemoryContext oldcontext,
 				aggcontext;
@@ -1570,6 +1645,9 @@ jsonb_agg_transfn(PG_FUNCTION_ARGS)
 		result = state->res;
 	}
 
+	if (absent_on_null && PG_ARGISNULL(1))
+		PG_RETURN_POINTER(state);
+
 	/* turn the argument into jsonb in the normal function context */
 
 	val = PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1);
@@ -1639,6 +1717,24 @@ jsonb_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+/*
+ * jsonb_agg aggregate function
+ */
+Datum
+jsonb_agg_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_agg_transfn_worker(fcinfo, false);
+}
+
+/*
+ * jsonb_agg_strict aggregate function
+ */
+Datum
+jsonb_agg_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_agg_transfn_worker(fcinfo, true);
+}
+
 Datum
 jsonb_agg_finalfn(PG_FUNCTION_ARGS)
 {
@@ -1672,11 +1768,9 @@ jsonb_agg_finalfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(out);
 }
 
-/*
- * jsonb_object_agg aggregate function
- */
-Datum
-jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
+static Datum
+jsonb_object_agg_transfn_worker(FunctionCallInfo fcinfo,
+								bool absent_on_null, bool unique_keys)
 {
 	MemoryContext oldcontext,
 				aggcontext;
@@ -1690,6 +1784,7 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 			   *jbval;
 	JsonbValue	v;
 	JsonbIteratorToken type;
+	bool		skip;
 
 	if (!AggCheckCallContext(fcinfo, &aggcontext))
 	{
@@ -1709,6 +1804,9 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 		state->res = result;
 		result->res = pushJsonbValue(&result->parseState,
 									 WJB_BEGIN_OBJECT, NULL);
+		result->parseState->unique_keys = unique_keys;
+		result->parseState->skip_nulls = absent_on_null;
+
 		MemoryContextSwitchTo(oldcontext);
 
 		arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);
@@ -1744,6 +1842,15 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("field name must not be null")));
 
+	/*
+	 * Skip null values if absent_on_null unless key uniqueness check is
+	 * needed (because we must save keys in this case).
+	 */
+	skip = absent_on_null && PG_ARGISNULL(2);
+
+	if (skip && !unique_keys)
+		PG_RETURN_POINTER(state);
+
 	val = PG_GETARG_DATUM(1);
 
 	memset(&elem, 0, sizeof(JsonbInState));
@@ -1799,6 +1906,16 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 				}
 				result->res = pushJsonbValue(&result->parseState,
 											 WJB_KEY, &v);
+
+				if (skip)
+				{
+					v.type = jbvNull;
+					result->res = pushJsonbValue(&result->parseState,
+												 WJB_VALUE, &v);
+					MemoryContextSwitchTo(oldcontext);
+					PG_RETURN_POINTER(state);
+				}
+
 				break;
 			case WJB_END_ARRAY:
 				break;
@@ -1871,6 +1988,43 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 	PG_RETURN_POINTER(state);
 }
 
+/*
+ * jsonb_object_agg aggregate function
+ */
+Datum
+jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_object_agg_transfn_worker(fcinfo, false, false);
+}
+
+
+/*
+ * jsonb_object_agg_strict aggregate function
+ */
+Datum
+jsonb_object_agg_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_object_agg_transfn_worker(fcinfo, true, false);
+}
+
+/*
+ * jsonb_object_agg_unique aggregate function
+ */
+Datum
+jsonb_object_agg_unique_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_object_agg_transfn_worker(fcinfo, false, true);
+}
+
+/*
+ * jsonb_object_agg_unique_strict aggregate function
+ */
+Datum
+jsonb_object_agg_unique_strict_transfn(PG_FUNCTION_ARGS)
+{
+	return jsonb_object_agg_transfn_worker(fcinfo, true, true);
+}
+
 Datum
 jsonb_object_agg_finalfn(PG_FUNCTION_ARGS)
 {
diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c
index e5b1ebf0c36..eefa429b9c3 100644
--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -64,7 +64,8 @@ static int	lengthCompareJsonbStringValue(const void *a, const void *b);
 static int	lengthCompareJsonbString(const char *val1, int len1,
 									 const char *val2, int len2);
 static int	lengthCompareJsonbPair(const void *a, const void *b, void *binequal);
-static void uniqueifyJsonbObject(JsonbValue *object);
+static void uniqueifyJsonbObject(JsonbValue *object, bool unique_keys,
+								 bool skip_nulls);
 static JsonbValue *pushJsonbValueScalar(JsonbParseState **pstate,
 										JsonbIteratorToken seq,
 										JsonbValue *scalarVal);
@@ -689,7 +690,9 @@ pushJsonbValueScalar(JsonbParseState **pstate, JsonbIteratorToken seq,
 			appendElement(*pstate, scalarVal);
 			break;
 		case WJB_END_OBJECT:
-			uniqueifyJsonbObject(&(*pstate)->contVal);
+			uniqueifyJsonbObject(&(*pstate)->contVal,
+								 (*pstate)->unique_keys,
+								 (*pstate)->skip_nulls);
 			/* fall through! */
 		case WJB_END_ARRAY:
 			/* Steps here common to WJB_END_OBJECT case */
@@ -732,6 +735,9 @@ pushState(JsonbParseState **pstate)
 	JsonbParseState *ns = palloc(sizeof(JsonbParseState));
 
 	ns->next = *pstate;
+	ns->unique_keys = false;
+	ns->skip_nulls = false;
+
 	return ns;
 }
 
@@ -1936,7 +1942,7 @@ lengthCompareJsonbPair(const void *a, const void *b, void *binequal)
  * Sort and unique-ify pairs in JsonbValue object
  */
 static void
-uniqueifyJsonbObject(JsonbValue *object)
+uniqueifyJsonbObject(JsonbValue *object, bool unique_keys, bool skip_nulls)
 {
 	bool		hasNonUniq = false;
 
@@ -1946,23 +1952,43 @@ uniqueifyJsonbObject(JsonbValue *object)
 		qsort_arg(object->val.object.pairs, object->val.object.nPairs, sizeof(JsonbPair),
 				  lengthCompareJsonbPair, &hasNonUniq);
 
-	if (hasNonUniq)
+	if (hasNonUniq && unique_keys)
+		ereport(ERROR,
+				errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
+				errmsg("duplicate JSON object key"));
+
+	if (hasNonUniq || skip_nulls)
 	{
-		JsonbPair  *ptr = object->val.object.pairs + 1,
-				   *res = object->val.object.pairs;
+		JsonbPair  *ptr,
+				   *res;
+
+		while (skip_nulls && object->val.object.nPairs > 0 &&
+			   object->val.object.pairs->value.type == jbvNull)
+		{
+			/* If skip_nulls is true, remove leading items with null */
+			object->val.object.pairs++;
+			object->val.object.nPairs--;
+		}
 
-		while (ptr - object->val.object.pairs < object->val.object.nPairs)
+		if (object->val.object.nPairs > 0)
 		{
-			/* Avoid copying over duplicate */
-			if (lengthCompareJsonbStringValue(ptr, res) != 0)
+			ptr = object->val.object.pairs + 1;
+			res = object->val.object.pairs;
+
+			while (ptr - object->val.object.pairs < object->val.object.nPairs)
 			{
-				res++;
-				if (ptr != res)
-					memcpy(res, ptr, sizeof(JsonbPair));
+				/* Avoid copying over duplicate or null */
+				if (lengthCompareJsonbStringValue(ptr, res) != 0 &&
+					(!skip_nulls || ptr->value.type != jbvNull))
+				{
+					res++;
+					if (ptr != res)
+						memcpy(res, ptr, sizeof(JsonbPair));
+				}
+				ptr++;
 			}
-			ptr++;
-		}
 
-		object->val.object.nPairs = res + 1 - object->val.object.pairs;
+			object->val.object.nPairs = res + 1 - object->val.object.pairs;
+		}
 	}
 }
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 4a98b82f07c..5f953338f3d 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -457,9 +457,15 @@ static void get_func_expr(FuncExpr *expr, deparse_context *context,
 						  bool showimplicit);
 static void get_agg_expr(Aggref *aggref, deparse_context *context,
 						 Aggref *original_aggref);
+static void get_agg_expr_helper(Aggref *aggref, deparse_context *context,
+								Aggref *original_aggref, const char *funcname,
+								const char *options, bool is_json_objectagg);
 static void get_agg_combine_expr(Node *node, deparse_context *context,
 								 void *callback_arg);
 static void get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context);
+static void get_windowfunc_expr_helper(WindowFunc *wfunc, deparse_context *context,
+									   const char *funcname, const char *options,
+									   bool is_json_objectagg);
 static bool get_func_sql_syntax(FuncExpr *expr, deparse_context *context);
 static void get_coercion_expr(Node *arg, deparse_context *context,
 							  Oid resulttype, int32 resulttypmod,
@@ -467,6 +473,15 @@ static void get_coercion_expr(Node *arg, deparse_context *context,
 static void get_const_expr(Const *constval, deparse_context *context,
 						   int showtype);
 static void get_const_collation(Const *constval, deparse_context *context);
+static void get_json_format(JsonFormat *format, StringInfo buf);
+static void get_json_constructor(JsonConstructorExpr *ctor,
+								 deparse_context *context, bool showimplicit);
+static void get_json_constructor_options(JsonConstructorExpr *ctor,
+										 StringInfo buf);
+static void get_json_agg_constructor(JsonConstructorExpr *ctor,
+									 deparse_context *context,
+									 const char *funcname,
+									 bool is_json_objectagg);
 static void simple_quote_literal(StringInfo buf, const char *val);
 static void get_sublink_expr(SubLink *sublink, deparse_context *context);
 static void get_tablefunc(TableFunc *tf, deparse_context *context,
@@ -6280,7 +6295,8 @@ get_rule_sortgroupclause(Index ref, List *tlist, bool force_colno,
 		bool		need_paren = (PRETTY_PAREN(context)
 								  || IsA(expr, FuncExpr)
 								  || IsA(expr, Aggref)
-								  || IsA(expr, WindowFunc));
+								  || IsA(expr, WindowFunc)
+								  || IsA(expr, JsonConstructorExpr));
 
 		if (need_paren)
 			appendStringInfoChar(context->buf, '(');
@@ -8117,6 +8133,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 		case T_GroupingFunc:
 		case T_WindowFunc:
 		case T_FuncExpr:
+		case T_JsonConstructorExpr:
 			/* function-like: name(..) or name[..] */
 			return true;
 
@@ -8292,6 +8309,11 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 					return false;
 			}
 
+		case T_JsonValueExpr:
+			/* maybe simple, check args */
+			return isSimpleNode((Node *) ((JsonValueExpr *) node)->raw_expr,
+								node, prettyFlags);
+
 		default:
 			break;
 	}
@@ -9495,6 +9517,19 @@ get_rule_expr(Node *node, deparse_context *context,
 			}
 			break;
 
+		case T_JsonValueExpr:
+			{
+				JsonValueExpr *jve = (JsonValueExpr *) node;
+
+				get_rule_expr((Node *) jve->raw_expr, context, false);
+				get_json_format(jve->format, context->buf);
+			}
+			break;
+
+		case T_JsonConstructorExpr:
+			get_json_constructor((JsonConstructorExpr *) node, context, false);
+			break;
+
 		case T_List:
 			{
 				char	   *sep;
@@ -9769,10 +9804,23 @@ static void
 get_agg_expr(Aggref *aggref, deparse_context *context,
 			 Aggref *original_aggref)
 {
+	get_agg_expr_helper(aggref, context, original_aggref, NULL, NULL,
+						false);
+}
+
+/*
+ * get_agg_expr_helper		- subroutine for get_agg_expr and
+ *							get_json_agg_constructor
+ */
+static void
+get_agg_expr_helper(Aggref *aggref, deparse_context *context,
+					Aggref *original_aggref, const char *funcname,
+					const char *options, bool is_json_objectagg)
+{
 	StringInfo	buf = context->buf;
 	Oid			argtypes[FUNC_MAX_ARGS];
 	int			nargs;
-	bool		use_variadic;
+	bool		use_variadic = false;
 
 	/*
 	 * For a combining aggregate, we look up and deparse the corresponding
@@ -9802,13 +9850,14 @@ get_agg_expr(Aggref *aggref, deparse_context *context,
 	/* Extract the argument types as seen by the parser */
 	nargs = get_aggregate_argtypes(aggref, argtypes);
 
+	if (!funcname)
+		funcname = generate_function_name(aggref->aggfnoid, nargs, NIL,
+										  argtypes, aggref->aggvariadic,
+										  &use_variadic,
+										  context->special_exprkind);
+
 	/* Print the aggregate name, schema-qualified if needed */
-	appendStringInfo(buf, "%s(%s",
-					 generate_function_name(aggref->aggfnoid, nargs,
-											NIL, argtypes,
-											aggref->aggvariadic,
-											&use_variadic,
-											context->special_exprkind),
+	appendStringInfo(buf, "%s(%s", funcname,
 					 (aggref->aggdistinct != NIL) ? "DISTINCT " : "");
 
 	if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
@@ -9844,7 +9893,21 @@ get_agg_expr(Aggref *aggref, deparse_context *context,
 				if (tle->resjunk)
 					continue;
 				if (i++ > 0)
-					appendStringInfoString(buf, ", ");
+				{
+					if (is_json_objectagg)
+					{
+						/*
+						 * the ABSENT ON NULL and WITH UNIQUE args are printed
+						 * separately, so ignore them here
+						 */
+						if (i > 2)
+							break;
+
+						appendStringInfoString(buf, " : ");
+					}
+					else
+						appendStringInfoString(buf, ", ");
+				}
 				if (use_variadic && i == nargs)
 					appendStringInfoString(buf, "VARIADIC ");
 				get_rule_expr(arg, context, true);
@@ -9858,6 +9921,9 @@ get_agg_expr(Aggref *aggref, deparse_context *context,
 		}
 	}
 
+	if (options)
+		appendStringInfoString(buf, options);
+
 	if (aggref->aggfilter != NULL)
 	{
 		appendStringInfoString(buf, ") FILTER (WHERE ");
@@ -9891,6 +9957,19 @@ get_agg_combine_expr(Node *node, deparse_context *context, void *callback_arg)
 static void
 get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 {
+	get_windowfunc_expr_helper(wfunc, context, NULL, NULL, false);
+}
+
+
+/*
+ * get_windowfunc_expr_helper	- subroutine for get_windowfunc_expr and
+ *								get_json_agg_constructor
+ */
+static void
+get_windowfunc_expr_helper(WindowFunc *wfunc, deparse_context *context,
+						   const char *funcname, const char *options,
+						   bool is_json_objectagg)
+{
 	StringInfo	buf = context->buf;
 	Oid			argtypes[FUNC_MAX_ARGS];
 	int			nargs;
@@ -9913,16 +9992,30 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		nargs++;
 	}
 
-	appendStringInfo(buf, "%s(",
-					 generate_function_name(wfunc->winfnoid, nargs,
-											argnames, argtypes,
-											false, NULL,
-											context->special_exprkind));
+	if (!funcname)
+		funcname = generate_function_name(wfunc->winfnoid, nargs, argnames,
+										  argtypes, false, NULL,
+										  context->special_exprkind);
+
+	appendStringInfo(buf, "%s(", funcname);
+
 	/* winstar can be set only in zero-argument aggregates */
 	if (wfunc->winstar)
 		appendStringInfoChar(buf, '*');
 	else
-		get_rule_expr((Node *) wfunc->args, context, true);
+	{
+		if (is_json_objectagg)
+		{
+			get_rule_expr((Node *) linitial(wfunc->args), context, false);
+			appendStringInfoString(buf, " : ");
+			get_rule_expr((Node *) lsecond(wfunc->args), context, false);
+		}
+		else
+			get_rule_expr((Node *) wfunc->args, context, true);
+	}
+
+	if (options)
+		appendStringInfoString(buf, options);
 
 	if (wfunc->aggfilter != NULL)
 	{
@@ -10484,6 +10577,158 @@ get_const_collation(Const *constval, deparse_context *context)
 }
 
 /*
+ * get_json_format			- Parse back a JsonFormat node
+ */
+static void
+get_json_format(JsonFormat *format, StringInfo buf)
+{
+	if (format->format_type == JS_FORMAT_DEFAULT)
+		return;
+
+	appendStringInfoString(buf,
+						   format->format_type == JS_FORMAT_JSONB ?
+						   " FORMAT JSONB" : " FORMAT JSON");
+
+	if (format->encoding != JS_ENC_DEFAULT)
+	{
+		const char *encoding;
+
+		encoding =
+			format->encoding == JS_ENC_UTF16 ? "UTF16" :
+			format->encoding == JS_ENC_UTF32 ? "UTF32" : "UTF8";
+
+		appendStringInfo(buf, " ENCODING %s", encoding);
+	}
+}
+
+/*
+ * get_json_returning		- Parse back a JsonReturning structure
+ */
+static void
+get_json_returning(JsonReturning *returning, StringInfo buf,
+				   bool json_format_by_default)
+{
+	if (!OidIsValid(returning->typid))
+		return;
+
+	appendStringInfo(buf, " RETURNING %s",
+					 format_type_with_typemod(returning->typid,
+											  returning->typmod));
+
+	if (!json_format_by_default ||
+		returning->format->format_type !=
+		(returning->typid == JSONBOID ? JS_FORMAT_JSONB : JS_FORMAT_JSON))
+		get_json_format(returning->format, buf);
+}
+
+/*
+ * get_json_constructor		- Parse back a JsonConstructorExpr node
+ */
+static void
+get_json_constructor(JsonConstructorExpr *ctor, deparse_context *context,
+					 bool showimplicit)
+{
+	StringInfo	buf = context->buf;
+	const char *funcname;
+	bool		is_json_object;
+	int			curridx;
+	ListCell   *lc;
+
+	if (ctor->type == JSCTOR_JSON_OBJECTAGG)
+	{
+		get_json_agg_constructor(ctor, context, "JSON_OBJECTAGG", true);
+		return;
+	}
+	else if (ctor->type == JSCTOR_JSON_ARRAYAGG)
+	{
+		get_json_agg_constructor(ctor, context, "JSON_ARRAYAGG", false);
+		return;
+	}
+
+	switch (ctor->type)
+	{
+		case JSCTOR_JSON_OBJECT:
+			funcname = "JSON_OBJECT";
+			break;
+		case JSCTOR_JSON_ARRAY:
+			funcname = "JSON_ARRAY";
+			break;
+		default:
+			elog(ERROR, "invalid JsonConstructorExprType %d", ctor->type);
+	}
+
+	appendStringInfo(buf, "%s(", funcname);
+
+	is_json_object = ctor->type == JSCTOR_JSON_OBJECT;
+	foreach(lc, ctor->args)
+	{
+		curridx = foreach_current_index(lc);
+		if (curridx > 0)
+		{
+			const char *sep;
+
+			sep = (is_json_object && (curridx % 2) != 0) ? " : " : ", ";
+			appendStringInfoString(buf, sep);
+		}
+
+		get_rule_expr((Node *) lfirst(lc), context, true);
+	}
+
+	get_json_constructor_options(ctor, buf);
+	appendStringInfo(buf, ")");
+}
+
+/*
+ * Append options, if any, to the JSON constructor being deparsed
+ */
+static void
+get_json_constructor_options(JsonConstructorExpr *ctor, StringInfo buf)
+{
+	if (ctor->absent_on_null)
+	{
+		if (ctor->type == JSCTOR_JSON_OBJECT ||
+			ctor->type == JSCTOR_JSON_OBJECTAGG)
+			appendStringInfoString(buf, " ABSENT ON NULL");
+	}
+	else
+	{
+		if (ctor->type == JSCTOR_JSON_ARRAY ||
+			ctor->type == JSCTOR_JSON_ARRAYAGG)
+			appendStringInfoString(buf, " NULL ON NULL");
+	}
+
+	if (ctor->unique)
+		appendStringInfoString(buf, " WITH UNIQUE KEYS");
+
+	get_json_returning(ctor->returning, buf, true);
+}
+
+/*
+ * get_json_agg_constructor - Parse back an aggregate JsonConstructorExpr node
+ */
+static void
+get_json_agg_constructor(JsonConstructorExpr *ctor, deparse_context *context,
+						 const char *funcname, bool is_json_objectagg)
+{
+	StringInfoData options;
+
+	initStringInfo(&options);
+	get_json_constructor_options(ctor, &options);
+
+	if (IsA(ctor->func, Aggref))
+		get_agg_expr_helper((Aggref *) ctor->func, context,
+							(Aggref *) ctor->func,
+							funcname, options.data, is_json_objectagg);
+	else if (IsA(ctor->func, WindowFunc))
+		get_windowfunc_expr_helper((WindowFunc *) ctor->func, context,
+								   funcname, options.data,
+								   is_json_objectagg);
+	else
+		elog(ERROR, "invalid JsonConstructorExpr underlying node type: %d",
+			 nodeTag(ctor->func));
+}
+
+/*
  * simple_quote_literal - Format a string as a SQL literal, append to buf
  */
 static void