Support multi-argument UNNEST(), and TABLE() syntax for multiple functions.

This patch adds the ability to write TABLE( function1(), function2(), ...)
as a single FROM-clause entry.  The result is the concatenation of the
first row from each function, followed by the second row from each
function, etc; with NULLs inserted if any function produces fewer rows than
others.  This is believed to be a much more useful behavior than what
Postgres currently does with multiple SRFs in a SELECT list.

This syntax also provides a reasonable way to combine use of column
definition lists with WITH ORDINALITY: put the column definition list
inside TABLE(), where it's clear that it doesn't control the ordinality
column as well.

Also implement SQL-compliant multiple-argument UNNEST(), by turning
UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)).

The SQL standard specifies TABLE() with only a single function, not
multiple functions, and it seems to require an implicit UNNEST() which is
not what this patch does.  There may be something wrong with that reading
of the spec, though, because if it's right then the spec's TABLE() is just
a pointless alternative spelling of UNNEST().  After further review of
that, we might choose to adopt a different syntax for what this patch does,
but in any case this functionality seems clearly worthwhile.

Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and
significantly revised by me

1 files changed, 19 insertions, 27 deletions

diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 4a7e793ae0a..d3ed4fe98b9 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -122,14 +122,10 @@ makeVarFromTargetEntry(Index varno,
  * a rowtype; either a named composite type, or RECORD.  This function
  * encapsulates the logic for determining the correct rowtype OID to use.
  *
- * If allowScalar is true, then for the case where the RTE is a function
+ * If allowScalar is true, then for the case where the RTE is a single function
  * returning a non-composite result type, we produce a normal Var referencing
  * the function's result directly, instead of the single-column composite
  * value that the whole-row notation might otherwise suggest.
- *
- * We also handle the specific case of function RTEs with ordinality,
- * where the additional column has to be added. This forces the result
- * to be composite and RECORD type.
  */
 Var *
 makeWholeRowVar(RangeTblEntry *rte,
@@ -139,6 +135,7 @@ makeWholeRowVar(RangeTblEntry *rte,
 {
 	Var		   *result;
 	Oid			toid;
+	Node	   *fexpr;
 
 	switch (rte->rtekind)
 	{
@@ -157,31 +154,27 @@ makeWholeRowVar(RangeTblEntry *rte,
 			break;
 
 		case RTE_FUNCTION:
+
 			/*
-			 * RTE is a function with or without ordinality. We map the
-			 * cases as follows:
-			 *
-			 * If ordinality is set, we return a composite var even if
-			 * the function is a scalar. This var is always of RECORD type.
-			 *
-			 * If ordinality is not set but the function returns a row,
-			 * we keep the function's return type.
-			 *
-			 * If the function is a scalar, we do what allowScalar requests.
+			 * If there's more than one function, or ordinality is requested,
+			 * force a RECORD result, since there's certainly more than one
+			 * column involved and it can't be a known named type.
 			 */
-			toid = exprType(rte->funcexpr);
-
-			if (rte->funcordinality)
+			if (rte->funcordinality || list_length(rte->functions) != 1)
 			{
-				/* ORDINALITY always produces an anonymous RECORD result */
+				/* always produces an anonymous RECORD result */
 				result = makeVar(varno,
 								 InvalidAttrNumber,
 								 RECORDOID,
 								 -1,
 								 InvalidOid,
 								 varlevelsup);
+				break;
 			}
-			else if (type_is_rowtype(toid))
+
+			fexpr = ((RangeTblFunction *) linitial(rte->functions))->funcexpr;
+			toid = exprType(fexpr);
+			if (type_is_rowtype(toid))
 			{
 				/* func returns composite; same as relation case */
 				result = makeVar(varno,
@@ -198,7 +191,7 @@ makeWholeRowVar(RangeTblEntry *rte,
 								 1,
 								 toid,
 								 -1,
-								 exprCollation(rte->funcexpr),
+								 exprCollation(fexpr),
 								 varlevelsup);
 			}
 			else
@@ -214,6 +207,7 @@ makeWholeRowVar(RangeTblEntry *rte,
 			break;
 
 		default:
+
 			/*
 			 * RTE is a join, subselect, or VALUES.  We represent this as a
 			 * whole-row Var of RECORD type. (Note that in most cases the Var
@@ -541,23 +535,21 @@ makeDefElemExtended(char *nameSpace, char *name, Node *arg,
  * makeFuncCall -
  *
  * Initialize a FuncCall struct with the information every caller must
- * supply.  Any non-default parameters have to be handled by the
- * caller.
- *
+ * supply.	Any non-default parameters have to be inserted by the caller.
  */
-
 FuncCall *
 makeFuncCall(List *name, List *args, int location)
 {
-	FuncCall *n = makeNode(FuncCall);
+	FuncCall   *n = makeNode(FuncCall);
+
 	n->funcname = name;
 	n->args = args;
-	n->location = location;
 	n->agg_order = NIL;
 	n->agg_filter = NULL;
 	n->agg_star = FALSE;
 	n->agg_distinct = FALSE;
 	n->func_variadic = FALSE;
 	n->over = NULL;
+	n->location = location;
 	return n;
 }