Reimplement CASE val WHEN compval1 THEN ... WHEN compval2 THEN ... END

so that the 'val' is computed only once, per recent discussion.  The
speedup is not much when 'val' is just a simple variable, but could be
significant for larger expressions.  More importantly this avoids issues
with multiple evaluations of a volatile 'val', and it allows the CASE
expression to be reverse-listed in its original form by ruleutils.c.

10 files changed, 194 insertions, 44 deletions

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 94a5c110d41..fc16cccdda9 100644
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.155 2004/03/17 01:02:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.156 2004/03/17 20:48:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -81,6 +81,9 @@ static Datum ExecEvalAnd(BoolExprState *andExpr, ExprContext *econtext,
 						 bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
 			 bool *isNull, ExprDoneCond *isDone);
+static Datum ExecEvalCaseTestExpr(ExprState *exprstate,
+								  ExprContext *econtext,
+								  bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalArray(ArrayExprState *astate,
 						   ExprContext *econtext,
 						   bool *isNull, ExprDoneCond *isDone);
@@ -1809,11 +1812,30 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
 {
 	List	   *clauses = caseExpr->args;
 	List	   *clause;
+	Datum		save_datum;
+	bool		save_isNull;
 
 	if (isDone)
 		*isDone = ExprSingleResult;
 
 	/*
+	 * If there's a test expression, we have to evaluate it and save
+	 * the value where the CaseTestExpr placeholders can find it.
+	 * We must save and restore prior setting of econtext's caseValue fields,
+	 * in case this node is itself within a larger CASE.
+	 */
+	save_datum = econtext->caseValue_datum;
+	save_isNull = econtext->caseValue_isNull;
+
+	if (caseExpr->arg)
+	{
+		econtext->caseValue_datum = ExecEvalExpr(caseExpr->arg,
+												 econtext,
+												 &econtext->caseValue_isNull,
+												 NULL);
+	}
+
+	/*
 	 * we evaluate each of the WHEN clauses in turn, as soon as one is
 	 * true we return the corresponding result. If none are true then we
 	 * return the value of the default clause, or NULL if there is none.
@@ -1835,6 +1857,8 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
 		 */
 		if (DatumGetBool(clause_value) && !*isNull)
 		{
+			econtext->caseValue_datum = save_datum;
+			econtext->caseValue_isNull = save_isNull;
 			return ExecEvalExpr(wclause->result,
 								econtext,
 								isNull,
@@ -1842,6 +1866,9 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
 		}
 	}
 
+	econtext->caseValue_datum = save_datum;
+	econtext->caseValue_isNull = save_isNull;
+
 	if (caseExpr->defresult)
 	{
 		return ExecEvalExpr(caseExpr->defresult,
@@ -1854,6 +1881,22 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
 	return (Datum) 0;
 }
 
+/*
+ * ExecEvalCaseTestExpr
+ *
+ * Return the value stored by CASE.
+ */
+static Datum
+ExecEvalCaseTestExpr(ExprState *exprstate,
+					 ExprContext *econtext,
+					 bool *isNull, ExprDoneCond *isDone)
+{
+	if (isDone)
+		*isDone = ExprSingleResult;
+	*isNull = econtext->caseValue_isNull;
+	return econtext->caseValue_datum;
+}
+
 /* ----------------------------------------------------------------
  *		ExecEvalArray - ARRAY[] expressions
  *
@@ -2478,6 +2521,10 @@ ExecInitExpr(Expr *node, PlanState *parent)
 			state = (ExprState *) makeNode(ExprState);
 			state->evalfunc = ExecEvalCoerceToDomainValue;
 			break;
+		case T_CaseTestExpr:
+			state = (ExprState *) makeNode(ExprState);
+			state->evalfunc = ExecEvalCaseTestExpr;
+			break;
 		case T_Aggref:
 			{
 				Aggref	   *aggref = (Aggref *) node;
@@ -2666,6 +2713,7 @@ ExecInitExpr(Expr *node, PlanState *parent)
 				List	   *inlist;
 
 				cstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecEvalCase;
+				cstate->arg = ExecInitExpr(caseexpr->arg, parent);
 				FastListInit(&outlist);
 				foreach(inlist, caseexpr->args)
 				{
@@ -2680,8 +2728,6 @@ ExecInitExpr(Expr *node, PlanState *parent)
 					FastAppend(&outlist, wstate);
 				}
 				cstate->args = FastListValue(&outlist);
-				/* caseexpr->arg should be null by now */
-				Assert(caseexpr->arg == NULL);
 				cstate->defresult = ExecInitExpr(caseexpr->defresult, parent);
 				state = (ExprState *) cstate;
 			}
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index b89f4015970..9702b1cf0aa 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execUtils.c,v 1.109 2004/01/22 02:23:21 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execUtils.c,v 1.110 2004/03/17 20:48:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -306,6 +306,9 @@ CreateExprContext(EState *estate)
 	econtext->ecxt_aggvalues = NULL;
 	econtext->ecxt_aggnulls = NULL;
 
+	econtext->caseValue_datum = (Datum) 0;
+	econtext->caseValue_isNull = true;
+
 	econtext->domainValue_datum = (Datum) 0;
 	econtext->domainValue_isNull = true;
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index c1c4ddfed8b..c7d6193280e 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.278 2004/03/11 01:47:35 ishii Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.279 2004/03/17 20:48:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -969,6 +969,20 @@ _copyCaseWhen(CaseWhen *from)
 }
 
 /*
+ * _copyCaseTestExpr
+ */
+static CaseTestExpr *
+_copyCaseTestExpr(CaseTestExpr *from)
+{
+	CaseTestExpr *newnode = makeNode(CaseTestExpr);
+
+	COPY_SCALAR_FIELD(typeId);
+	COPY_SCALAR_FIELD(typeMod);
+
+	return newnode;
+}
+
+/*
  * _copyArrayExpr
  */
 static ArrayExpr *
@@ -2643,6 +2657,9 @@ copyObject(void *from)
 		case T_CaseWhen:
 			retval = _copyCaseWhen(from);
 			break;
+		case T_CaseTestExpr:
+			retval = _copyCaseTestExpr(from);
+			break;
 		case T_ArrayExpr:
 			retval = _copyArrayExpr(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index fadd02c9357..900d98dc8c0 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.217 2004/03/14 23:41:26 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.218 2004/03/17 20:48:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -404,6 +404,15 @@ _equalCaseWhen(CaseWhen *a, CaseWhen *b)
 }
 
 static bool
+_equalCaseTestExpr(CaseTestExpr *a, CaseTestExpr *b)
+{
+	COMPARE_SCALAR_FIELD(typeId);
+	COMPARE_SCALAR_FIELD(typeMod);
+
+	return true;
+}
+
+static bool
 _equalArrayExpr(ArrayExpr *a, ArrayExpr *b)
 {
 	COMPARE_SCALAR_FIELD(array_typeid);
@@ -1724,6 +1733,9 @@ equal(void *a, void *b)
 		case T_CaseWhen:
 			retval = _equalCaseWhen(a, b);
 			break;
+		case T_CaseTestExpr:
+			retval = _equalCaseTestExpr(a, b);
+			break;
 		case T_ArrayExpr:
 			retval = _equalArrayExpr(a, b);
 			break;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 93afd868f87..4db6517cd76 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.232 2004/01/31 05:09:40 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.233 2004/03/17 20:48:42 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -806,6 +806,15 @@ _outCaseWhen(StringInfo str, CaseWhen *node)
 }
 
 static void
+_outCaseTestExpr(StringInfo str, CaseTestExpr *node)
+{
+	WRITE_NODE_TYPE("CASETESTEXPR");
+
+	WRITE_OID_FIELD(typeId);
+	WRITE_INT_FIELD(typeMod);
+}
+
+static void
 _outArrayExpr(StringInfo str, ArrayExpr *node)
 {
 	WRITE_NODE_TYPE("ARRAY");
@@ -1701,6 +1710,9 @@ _outNode(StringInfo str, void *obj)
 			case T_CaseWhen:
 				_outCaseWhen(str, obj);
 				break;
+			case T_CaseTestExpr:
+				_outCaseTestExpr(str, obj);
+				break;
 			case T_ArrayExpr:
 				_outArrayExpr(str, obj);
 				break;
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 93c71fd2247..116345686bf 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.165 2004/01/14 23:01:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.166 2004/03/17 20:48:42 tgl Exp $
  *
  * NOTES
  *	  Path and Plan nodes do not have any readfuncs support, because we
@@ -649,6 +649,20 @@ _readCaseWhen(void)
 }
 
 /*
+ * _readCaseTestExpr
+ */
+static CaseTestExpr *
+_readCaseTestExpr(void)
+{
+	READ_LOCALS(CaseTestExpr);
+
+	READ_OID_FIELD(typeId);
+	READ_INT_FIELD(typeMod);
+
+	READ_DONE();
+}
+
+/*
  * _readArrayExpr
  */
 static ArrayExpr *
@@ -1010,6 +1024,8 @@ parseNodeString(void)
 		return_value = _readCaseExpr();
 	else if (MATCH("WHEN", 4))
 		return_value = _readCaseWhen();
+	else if (MATCH("CASETESTEXPR", 12))
+		return_value = _readCaseTestExpr();
 	else if (MATCH("ARRAY", 5))
 		return_value = _readArrayExpr();
 	else if (MATCH("COALESCE", 8))
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 1f3a8afc7f4..1487aec453d 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.164 2004/03/14 23:41:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.165 2004/03/17 20:48:42 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1397,15 +1397,29 @@ eval_const_expressions_mutator(Node *node, List *active_fns)
 		 * simplify the entire CASE to that alternative's expression.
 		 * If there are no non-FALSE alternatives, we simplify the entire
 		 * CASE to the default result (ELSE result).
+		 *
+		 * If we have a simple-form CASE with constant test expression and
+		 * one or more constant comparison expressions, we could run the
+		 * implied comparisons and potentially reduce those arms to constants.
+		 * This is not yet implemented, however.  At present, the
+		 * CaseTestExpr placeholder will always act as a non-constant node
+		 * and prevent the comparison boolean expressions from being reduced
+		 * to Const nodes.
 		 *----------
 		 */
 		CaseExpr   *caseexpr = (CaseExpr *) node;
 		CaseExpr   *newcase;
+		Node	   *newarg;
 		FastList	newargs;
 		Node	   *defresult;
 		Const	   *const_input;
 		List	   *arg;
 
+		/* Simplify the test expression, if any */
+		newarg = eval_const_expressions_mutator((Node *) caseexpr->arg,
+												active_fns);
+
+		/* Simplify the WHEN clauses */
 		FastListInit(&newargs);
 		foreach(arg, caseexpr->args)
 		{
@@ -1454,7 +1468,7 @@ eval_const_expressions_mutator(Node *node, List *active_fns)
 		/* Otherwise we need a new CASE node */
 		newcase = makeNode(CaseExpr);
 		newcase->casetype = caseexpr->casetype;
-		newcase->arg = NULL;
+		newcase->arg = (Expr *) newarg;
 		newcase->args = FastListValue(&newargs);
 		newcase->defresult = (Expr *) defresult;
 		return (Node *) newcase;
@@ -2319,6 +2333,7 @@ expression_tree_walker(Node *node,
 		case T_Const:
 		case T_Param:
 		case T_CoerceToDomainValue:
+		case T_CaseTestExpr:
 		case T_SetToDefault:
 		case T_RangeTblRef:
 			/* primitive node types with no subnodes */
@@ -2425,6 +2440,8 @@ expression_tree_walker(Node *node,
 			{
 				CaseExpr   *caseexpr = (CaseExpr *) node;
 
+				if (walker(caseexpr->arg, context))
+					return true;
 				/* we assume walker doesn't care about CaseWhens, either */
 				foreach(temp, caseexpr->args)
 				{
@@ -2436,9 +2453,6 @@ expression_tree_walker(Node *node,
 					if (walker(when->result, context))
 						return true;
 				}
-				/* caseexpr->arg should be null, but we'll check it anyway */
-				if (walker(caseexpr->arg, context))
-					return true;
 				if (walker(caseexpr->defresult, context))
 					return true;
 			}
@@ -2692,6 +2706,7 @@ expression_tree_mutator(Node *node,
 		case T_Const:
 		case T_Param:
 		case T_CoerceToDomainValue:
+		case T_CaseTestExpr:
 		case T_SetToDefault:
 		case T_RangeTblRef:
 			/* primitive node types with no subnodes */
@@ -2829,9 +2844,8 @@ expression_tree_mutator(Node *node,
 				CaseExpr   *newnode;
 
 				FLATCOPY(newnode, caseexpr, CaseExpr);
-				MUTATE(newnode->args, caseexpr->args, List *);
-				/* caseexpr->arg should be null, but we'll check it anyway */
 				MUTATE(newnode->arg, caseexpr->arg, Expr *);
+				MUTATE(newnode->args, caseexpr->args, List *);
 				MUTATE(newnode->defresult, caseexpr->defresult, Expr *);
 				return (Node *) newnode;
 			}
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 9fd2e5b5795..e8abfe039f0 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.448 2004/03/11 01:47:37 ishii Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.449 2004/03/17 20:48:42 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -6965,6 +6965,7 @@ in_expr:	select_with_parens
 case_expr:	CASE case_arg when_clause_list case_default END_P
 				{
 					CaseExpr *c = makeNode(CaseExpr);
+					c->casetype = InvalidOid; /* not analyzed yet */
 					c->arg = (Expr *) $2;
 					c->args = $3;
 					c->defresult = (Expr *) $4;
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index c23e39a25d0..3881cc39538 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.165 2004/02/13 01:08:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.166 2004/03/17 20:48:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -637,14 +637,39 @@ transformExpr(ParseState *pstate, Node *expr)
 		case T_CaseExpr:
 			{
 				CaseExpr   *c = (CaseExpr *) expr;
-				CaseExpr   *newc = makeNode(CaseExpr);
-				List	   *newargs = NIL;
-				List	   *typeids = NIL;
+				CaseExpr   *newc;
+				Node	   *arg;
+				CaseTestExpr *placeholder;
+				List	   *newargs;
+				List	   *typeids;
 				List	   *args;
 				Node	   *defresult;
 				Oid			ptype;
 
+				/* If we already transformed this node, do nothing */
+				if (OidIsValid(c->casetype))
+				{
+					result = expr;
+					break;
+				}
+				newc = makeNode(CaseExpr);
+
+				/* transform the test expression, if any */
+				arg = transformExpr(pstate, (Node *) c->arg);
+				newc->arg = (Expr *) arg;
+				/* generate placeholder for test expression */
+				if (arg)
+				{
+					placeholder = makeNode(CaseTestExpr);
+					placeholder->typeId = exprType(arg);
+					placeholder->typeMod = exprTypmod(arg);
+				}
+				else
+					placeholder = NULL;
+
 				/* transform the list of arguments */
+				newargs = NIL;
+				typeids = NIL;
 				foreach(args, c->args)
 				{
 					CaseWhen   *w = (CaseWhen *) lfirst(args);
@@ -654,11 +679,11 @@ transformExpr(ParseState *pstate, Node *expr)
 					Assert(IsA(w, CaseWhen));
 
 					warg = (Node *) w->expr;
-					if (c->arg != NULL)
+					if (placeholder)
 					{
 						/* shorthand form was specified, so expand... */
 						warg = (Node *) makeSimpleA_Expr(AEXPR_OP, "=",
-														 (Node *) c->arg,
+														 (Node *) placeholder,
 														 warg);
 					}
 					neww->expr = (Expr *) transformExpr(pstate, warg);
@@ -667,18 +692,7 @@ transformExpr(ParseState *pstate, Node *expr)
 													 (Node *) neww->expr,
 															"CASE/WHEN");
 
-					/*
-					 * result is NULL for NULLIF() construct - thomas
-					 * 1998-11-11
-					 */
 					warg = (Node *) w->result;
-					if (warg == NULL)
-					{
-						A_Const    *n = makeNode(A_Const);
-
-						n->val.type = T_Null;
-						warg = (Node *) n;
-					}
 					neww->result = (Expr *) transformExpr(pstate, warg);
 
 					newargs = lappend(newargs, neww);
@@ -687,13 +701,6 @@ transformExpr(ParseState *pstate, Node *expr)
 
 				newc->args = newargs;
 
-				/*
-				 * It's not shorthand anymore, so drop the implicit
-				 * argument. This is necessary to keep any re-application
-				 * of transformExpr from doing the wrong thing.
-				 */
-				newc->arg = NULL;
-
 				/* transform the default clause */
 				defresult = (Node *) c->defresult;
 				if (defresult == NULL)
@@ -714,6 +721,7 @@ transformExpr(ParseState *pstate, Node *expr)
 				typeids = lconso(exprType((Node *) newc->defresult), typeids);
 
 				ptype = select_common_type(typeids, "CASE");
+				Assert(OidIsValid(ptype));
 				newc->casetype = ptype;
 
 				/* Convert default result clause, if necessary */
@@ -915,6 +923,7 @@ transformExpr(ParseState *pstate, Node *expr)
 		case T_BoolExpr:
 		case T_FieldSelect:
 		case T_RelabelType:
+		case T_CaseTestExpr:
 		case T_CoerceToDomain:
 		case T_CoerceToDomainValue:
 		case T_SetToDefault:
@@ -1288,6 +1297,9 @@ exprType(Node *expr)
 		case T_CaseWhen:
 			type = exprType((Node *) ((CaseWhen *) expr)->result);
 			break;
+		case T_CaseTestExpr:
+			type = ((CaseTestExpr *) expr)->typeId;
+			break;
 		case T_ArrayExpr:
 			type = ((ArrayExpr *) expr)->array_typeid;
 			break;
@@ -1408,6 +1420,8 @@ exprTypmod(Node *expr)
 				return typmod;
 			}
 			break;
+		case T_CaseTestExpr:
+			return ((CaseTestExpr *) expr)->typeMod;
 		case T_CoalesceExpr:
 			{
 				/*
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 7e1513796db..3960152f387 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -3,7 +3,7 @@
  *				back to source text
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.162 2004/01/31 05:09:40 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.163 2004/03/17 20:48:42 tgl Exp $
  *
  *	  This software is copyrighted by Jan Wieck - Hamburg.
  *
@@ -2564,7 +2564,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_ArrayExpr:		/* other separators */
 				case T_CoalesceExpr:	/* own parentheses */
 				case T_NullIfExpr:		/* other separators */
-				case T_Aggref:	/* own parentheses */
+				case T_Aggref:			/* own parentheses */
 				case T_CaseExpr:		/* other separators */
 					return true;
 				default:
@@ -2610,7 +2610,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_ArrayExpr:		/* other separators */
 				case T_CoalesceExpr:	/* own parentheses */
 				case T_NullIfExpr:		/* other separators */
-				case T_Aggref:	/* own parentheses */
+				case T_Aggref:			/* own parentheses */
 				case T_CaseExpr:		/* other separators */
 					return true;
 				default:
@@ -3026,6 +3026,11 @@ get_rule_expr(Node *node, deparse_context *context,
 
 				appendContextKeyword(context, "CASE",
 									 0, PRETTYINDENT_VAR, 0);
+				if (caseexpr->arg)
+				{
+					appendStringInfoChar(buf, ' ');
+					get_rule_expr((Node *) caseexpr->arg, context, true);
+				}
 				foreach(temp, caseexpr->args)
 				{
 					CaseWhen   *when = (CaseWhen *) lfirst(temp);
@@ -3034,7 +3039,17 @@ get_rule_expr(Node *node, deparse_context *context,
 						appendStringInfoChar(buf, ' ');
 					appendContextKeyword(context, "WHEN ",
 										 0, 0, 0);
-					get_rule_expr((Node *) when->expr, context, false);
+					if (caseexpr->arg)
+					{
+						/* Show only the RHS of "CaseTestExpr = RHS" */
+						Node   *rhs;
+
+						Assert(IsA(when->expr, OpExpr));
+						rhs = (Node *) lsecond(((OpExpr *) when->expr)->args);
+						get_rule_expr(rhs, context, false);
+					}
+					else
+						get_rule_expr((Node *) when->expr, context, false);
 					appendStringInfo(buf, " THEN ");
 					get_rule_expr((Node *) when->result, context, true);
 				}