CREATE STATISTICS: improve misleading error message

The previous change (commit f225473cba) was still not on target,
because it talked about relation kinds, which are not what is being
checked here.  Provide a more accurate message.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxEZ48toGH0Em_6vdsT57Y3L8pLF=DZCQ_gCii6=C3MeXw@mail.gmail.com

src/backend/tcop/utility.c

@@ -1863,8 +1863,7 @@ ProcessUtilitySlow(ParseState *pstate,
 					if (!IsA(rel, RangeVar))
 						ereport(ERROR,
 								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-								 errmsg("cannot create statistics on the specified relation"),
-								 errdetail("CREATE STATISTICS only supports tables, foreign tables and materialized views.")));
+								 errmsg("CREATE STATISTICS only supports relation names in the FROM clause")));
 
 					/*
 					 * CREATE STATISTICS will influence future execution plans

src/test/regress/expected/stats_ext.out

@@ -56,26 +56,20 @@ CREATE STATISTICS tst (unrecognized) ON x, y FROM ext_stats_test;
 ERROR:  unrecognized statistics kind "unrecognized"
 -- unsupported targets
 CREATE STATISTICS tst ON a FROM (VALUES (x)) AS foo;
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE STATISTICS tst ON a FROM foo NATURAL JOIN bar;
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE STATISTICS tst ON a FROM (SELECT * FROM ext_stats_test) AS foo;
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE STATISTICS tst ON a FROM ext_stats_test s TABLESAMPLE system (x);
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE STATISTICS tst ON a FROM XMLTABLE('foo' PASSING 'bar' COLUMNS a text);
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE FUNCTION tftest(int) returns table(a int, b int) as $$
 SELECT $1, $1+i FROM generate_series(1,5) g(i);
 $$ LANGUAGE sql IMMUTABLE STRICT;
 CREATE STATISTICS alt_stat2 ON a FROM tftest(1);
-ERROR:  cannot create statistics on the specified relation
-DETAIL:  CREATE STATISTICS only supports tables, foreign tables and materialized views.
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 DROP FUNCTION tftest;
 -- incorrect expressions
 CREATE STATISTICS tst ON (y) FROM ext_stats_test; -- single column reference