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

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -5087,12 +5087,12 @@ SELECT ft1.c1 FROM ft1 JOIN ft2 on ft1.c1 = ft2.c1 WHERE
 EXPLAIN (verbose, costs off)
 INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
                                                                                                                                QUERY PLAN                                                                                                                               
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Insert on public.ft2
    Remote SQL: INSERT INTO "S 1"."T 1"("C 1", c2, c3, c4, c5, c6, c7, c8) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
    Batch Size: 1
-   ->  Subquery Scan on "*SELECT*"
-         Output: "*SELECT*"."?column?", "*SELECT*"."?column?_1", NULL::integer, "*SELECT*"."?column?_2", NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying(10), 'ft2       '::character(10), NULL::user_enum
+   ->  Subquery Scan on unnamed_subquery
+         Output: unnamed_subquery."?column?", unnamed_subquery."?column?_1", NULL::integer, unnamed_subquery."?column?_2", NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying(10), 'ft2       '::character(10), NULL::user_enum
          ->  Foreign Scan on public.ft2 ft2_1
                Output: (ft2_1.c1 + 1000), (ft2_1.c2 + 100), (ft2_1.c3 || ft2_1.c3)
                Remote SQL: SELECT "C 1", c2, c3 FROM "S 1"."T 1" LIMIT 20::bigint

src/backend/executor/functions.c

@@ -2483,7 +2483,7 @@ tlist_coercion_finished:
 		rte = makeNode(RangeTblEntry);
 		rte->rtekind = RTE_SUBQUERY;
 		rte->subquery = parse;
-		rte->eref = rte->alias = makeAlias("*SELECT*", colnames);
+		rte->eref = makeAlias("unnamed_subquery", colnames);
 		rte->lateral = false;
 		rte->inh = false;
 		rte->inFromCl = true;

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);
 

src/test/regress/expected/partition_prune.out

@@ -4763,7 +4763,7 @@ select min(a) over (partition by a order by a) from part_abc where a >= stable_o
                                           QUERY PLAN                                          
 ----------------------------------------------------------------------------------------------
  Append
-   ->  Subquery Scan on "*SELECT* 1_1"
+   ->  Subquery Scan on unnamed_subquery_2
          ->  WindowAgg
                Window: w1 AS (PARTITION BY part_abc.a ORDER BY part_abc.a)
                ->  Append
@@ -4780,7 +4780,7 @@ select min(a) over (partition by a order by a) from part_abc where a >= stable_o
                            ->  Index Scan using part_abc_3_2_a_idx on part_abc_3_2 part_abc_4
                                  Index Cond: (a >= (stable_one() + 1))
                                  Filter: (d <= stable_one())
-   ->  Subquery Scan on "*SELECT* 2"
+   ->  Subquery Scan on unnamed_subquery_1
          ->  WindowAgg
                Window: w1 AS (PARTITION BY part_abc_5.a ORDER BY part_abc_5.a)
                ->  Append

src/test/regress/expected/rangefuncs.out

@@ -2131,9 +2131,9 @@ select testrngfunc();
 explain (verbose, costs off)
 select * from testrngfunc();
                               QUERY PLAN                              
-----------------------------------------------------------
- Subquery Scan on "*SELECT*"
-   Output: "*SELECT*"."?column?", "*SELECT*"."?column?_1"
+----------------------------------------------------------------------
+ Subquery Scan on unnamed_subquery
+   Output: unnamed_subquery."?column?", unnamed_subquery."?column?_1"
    ->  Unique
          Output: (1), (2)
          ->  Sort

src/test/regress/expected/union.out

@@ -942,7 +942,7 @@ SELECT q1 FROM int8_tbl EXCEPT SELECT q2 FROM int8_tbl ORDER BY q2 LIMIT 1;
 ERROR:  column "q2" does not exist
 LINE 1: ... int8_tbl EXCEPT SELECT q2 FROM int8_tbl ORDER BY q2 LIMIT 1...
                                                              ^
-DETAIL:  There is a column named "q2" in table "*SELECT* 2", but it cannot be referenced from this part of the query.
+DETAIL:  There is a column named "q2" in table "unnamed_subquery", but it cannot be referenced from this part of the query.
 -- But this should work:
 SELECT q1 FROM int8_tbl EXCEPT (((SELECT q2 FROM int8_tbl ORDER BY q2 LIMIT 1))) ORDER BY 1;
         q1        
@@ -1338,14 +1338,14 @@ where q2 = q2;
 ----------------------------------------------------------
  Unique
    ->  Merge Append
-         Sort Key: "*SELECT* 1".q1
-         ->  Subquery Scan on "*SELECT* 1"
+         Sort Key: unnamed_subquery.q1
+         ->  Subquery Scan on unnamed_subquery
                ->  Unique
                      ->  Sort
                            Sort Key: i81.q1, i81.q2
                            ->  Seq Scan on int8_tbl i81
                                  Filter: (q2 IS NOT NULL)
-         ->  Subquery Scan on "*SELECT* 2"
+         ->  Subquery Scan on unnamed_subquery_1
                ->  Unique
                      ->  Sort
                            Sort Key: i82.q1, i82.q2
@@ -1374,14 +1374,14 @@ where -q1 = q2;
 --------------------------------------------------------
  Unique
    ->  Merge Append
-         Sort Key: "*SELECT* 1".q1
-         ->  Subquery Scan on "*SELECT* 1"
+         Sort Key: unnamed_subquery.q1
+         ->  Subquery Scan on unnamed_subquery
                ->  Unique
                      ->  Sort
                            Sort Key: i81.q1, i81.q2
                            ->  Seq Scan on int8_tbl i81
                                  Filter: ((- q1) = q2)
-         ->  Subquery Scan on "*SELECT* 2"
+         ->  Subquery Scan on unnamed_subquery_1
                ->  Unique
                      ->  Sort
                            Sort Key: i82.q1, i82.q2