Add select_common_typmod()

This accompanies select_common_type() and select_common_collation().
Typmods were previously combined using hand-coded logic in several
places.  The logic in select_common_typmod() isn't very exciting, but
it makes the code more compact and readable in a few locations, and in
the future we can perhaps do more complicated things if desired.

As a small enhancement, the type unification of the direct and
aggregate arguments of hypothetical-set aggregates now unifies the
typmod as well using this new function, instead of just dropping it.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/97df3af9-8b5e-fb7f-a029-3eb7e80d7af9@2ndquadrant.com

src/backend/parser/analyze.c

@@ -1434,9 +1434,8 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 	for (i = 0; i < sublist_length; i++)
 	{
 		Oid			coltype;
-		int32		coltypmod = -1;
+		int32		coltypmod;
 		Oid			colcoll;
-		bool		first = true;
 
 		coltype = select_common_type(pstate, colexprs[i], "VALUES", NULL);
 
@@ -1446,19 +1445,9 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 
 			col = coerce_to_common_type(pstate, col, coltype, "VALUES");
 			lfirst(lc) = (void *) col;
-			if (first)
-			{
-				coltypmod = exprTypmod(col);
-				first = false;
-			}
-			else
-			{
-				/* As soon as we see a non-matching typmod, fall back to -1 */
-				if (coltypmod >= 0 && coltypmod != exprTypmod(col))
-					coltypmod = -1;
-			}
 		}
 
+		coltypmod = select_common_typmod(pstate, colexprs[i], coltype);
 		colcoll = select_common_collation(pstate, colexprs[i], true);
 
 		coltypes = lappend_oid(coltypes, coltype);
@@ -2020,8 +2009,6 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 			Node	   *rcolnode = (Node *) rtle->expr;
 			Oid			lcoltype = exprType(lcolnode);
 			Oid			rcoltype = exprType(rcolnode);
-			int32		lcoltypmod = exprTypmod(lcolnode);
-			int32		rcoltypmod = exprTypmod(rcolnode);
 			Node	   *bestexpr;
 			int			bestlocation;
 			Oid			rescoltype;
@@ -2034,11 +2021,6 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 											context,
 											&bestexpr);
 			bestlocation = exprLocation(bestexpr);
-			/* if same type and same typmod, use typmod; else default */
-			if (lcoltype == rcoltype && lcoltypmod == rcoltypmod)
-				rescoltypmod = lcoltypmod;
-			else
-				rescoltypmod = -1;
 
 			/*
 			 * Verify the coercions are actually possible.  If not, we'd fail
@@ -2089,6 +2071,10 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 				rtle->expr = (Expr *) rcolnode;
 			}
 
+			rescoltypmod = select_common_typmod(pstate,
+												list_make2(lcolnode, rcolnode),
+												rescoltype);
+
 			/*
 			 * Select common collation.  A common collation is required for
 			 * all set operators except UNION ALL; see SQL:2008 7.13 <query

src/backend/parser/parse_clause.c

@@ -1568,24 +1568,13 @@ buildMergedJoinVar(ParseState *pstate, JoinType jointype,
 			   *r_node,
 			   *res_node;
 
-	/*
-	 * Choose output type if input types are dissimilar.
-	 */
-	outcoltype = l_colvar->vartype;
-	outcoltypmod = l_colvar->vartypmod;
-	if (outcoltype != r_colvar->vartype)
-	{
-		outcoltype = select_common_type(pstate,
+	outcoltype = select_common_type(pstate,
+									list_make2(l_colvar, r_colvar),
+									"JOIN/USING",
+									NULL);
+	outcoltypmod = select_common_typmod(pstate,
 										list_make2(l_colvar, r_colvar),
-										"JOIN/USING",
-										NULL);
-		outcoltypmod = -1;		/* ie, unknown */
-	}
-	else if (outcoltypmod != r_colvar->vartypmod)
-	{
-		/* same type, but not same typmod */
-		outcoltypmod = -1;		/* ie, unknown */
-	}
+										outcoltype);
 
 	/*
 	 * Insert coercion functions if needed.  Note that a difference in typmod

src/backend/parser/parse_coerce.c

@@ -1522,6 +1522,43 @@ coerce_to_common_type(ParseState *pstate, Node *node,
 	return node;
 }
 
+/*
+ * select_common_typmod()
+ *		Determine the common typmod of a list of input expressions.
+ *
+ * common_type is the selected common type of the expressions, typically
+ * computed using select_common_type().
+ */
+int32
+select_common_typmod(ParseState *pstate, List *exprs, Oid common_type)
+{
+	ListCell   *lc;
+	bool		first = true;
+	int32		result = -1;
+
+	foreach(lc, exprs)
+	{
+		Node   *expr = (Node *) lfirst(lc);
+
+		/* Types must match */
+		if (exprType(expr) != common_type)
+			return -1;
+		else if (first)
+		{
+			result = exprTypmod(expr);
+			first = false;
+		}
+		else
+		{
+			/* As soon as we see a non-matching typmod, fall back to -1 */
+			if (result != exprTypmod(expr))
+				return -1;
+		}
+	}
+
+	return result;
+}
+
 /*
  * check_generic_type_consistency()
  *		Are the actual arguments potentially compatible with a

src/backend/parser/parse_func.c

@@ -1750,6 +1750,7 @@ unify_hypothetical_args(ParseState *pstate,
 		ListCell   *harg = list_nth_cell(fargs, hargpos);
 		ListCell   *aarg = list_nth_cell(fargs, aargpos);
 		Oid			commontype;
+		int32		commontypmod;
 
 		/* A mismatch means AggregateCreate didn't check properly ... */
 		if (declared_arg_types[hargpos] != declared_arg_types[aargpos])
@@ -1768,6 +1769,9 @@ unify_hypothetical_args(ParseState *pstate,
 										list_make2(lfirst(aarg), lfirst(harg)),
 										"WITHIN GROUP",
 										NULL);
+		commontypmod = select_common_typmod(pstate,
+											list_make2(lfirst(aarg), lfirst(harg)),
+											commontype);
 
 		/*
 		 * Perform the coercions.  We don't need to worry about NamedArgExprs
@@ -1776,7 +1780,7 @@ unify_hypothetical_args(ParseState *pstate,
 		lfirst(harg) = coerce_type(pstate,
 								   (Node *) lfirst(harg),
 								   actual_arg_types[hargpos],
-								   commontype, -1,
+								   commontype, commontypmod,
 								   COERCION_IMPLICIT,
 								   COERCE_IMPLICIT_CAST,
 								   -1);
@@ -1784,7 +1788,7 @@ unify_hypothetical_args(ParseState *pstate,
 		lfirst(aarg) = coerce_type(pstate,
 								   (Node *) lfirst(aarg),
 								   actual_arg_types[aargpos],
-								   commontype, -1,
+								   commontype, commontypmod,
 								   COERCION_IMPLICIT,
 								   COERCE_IMPLICIT_CAST,
 								   -1);

src/include/parser/parse_coerce.h

@@ -71,6 +71,8 @@ extern Node *coerce_to_common_type(ParseState *pstate, Node *node,
 								   Oid targetTypeId,
 								   const char *context);
 
+extern int32 select_common_typmod(ParseState *pstate, List *exprs, Oid common_type);
+
 extern bool check_generic_type_consistency(const Oid *actual_arg_types,
 										   const Oid *declared_arg_types,
 										   int nargs);