Don't generate fake "*SELECT*" or "*SELECT* %d" subquery aliases.

rte->alias should point only to a user-written alias, but in these
cases that principle was violated. Fixing this causes some regression
test output changes: wherever rte->alias previously had a value and
is now NULL, rte->eref is now set to a generated name rather than to
rte->alias; and the scheme used to generate eref names differs from
what we were doing for aliases.

The upshot is that instead of "*SELECT*" or "*SELECT* %d",
EXPLAIN will now emit "unnamed_subquery" or "unnamed_subquery_%d".
But that's a reasonable descriptor, and we were already producing
that in yet other cases, so this seems not too objectionable.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Co-authored-by: Robert Haas <rhaas@postgresql.org>
Discussion: https://postgr.es/m/CA+TgmoYSYmDA2GvanzPMci084n+mVucv0bJ0HPbs6uhmMN6HMg@mail.gmail.com

src/backend/parser/analyze.c

@@ -777,7 +777,7 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 		 */
 		nsitem = addRangeTableEntryForSubquery(pstate,
 											   selectQuery,
-											   makeAlias("*SELECT*", NIL),
+											   NULL,
 											   false,
 											   false);
 		addNSItemToQuery(pstate, nsitem, true, false, false);
@@ -2100,7 +2100,6 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 	{
 		/* Process leaf SELECT */
 		Query	   *selectQuery;
-		char		selectName[32];
 		ParseNamespaceItem *nsitem;
 		RangeTblRef *rtr;
 		ListCell   *tl;
@@ -2156,11 +2155,9 @@ transformSetOperationTree(ParseState *pstate, SelectStmt *stmt,
 		/*
 		 * Make the leaf query be a subquery in the top-level rangetable.
 		 */
-		snprintf(selectName, sizeof(selectName), "*SELECT* %d",
-				 list_length(pstate->p_rtable) + 1);
 		nsitem = addRangeTableEntryForSubquery(pstate,
 											   selectQuery,
-											   makeAlias(selectName, NIL),
+											   NULL,
 											   false,
 											   false);