Add more tests for CREATE TABLE AS with WITH NO DATA

The relation creation is done at executor startup, however the main
regression test suite is lacking scenarios where no data is inserted
which is something that can happen when using EXECUTE or EXPLAIN with
CREATE TABLE AS and WITH NO DATA.

Some patches are worked on to reshape the way CTAS relations are
created, so this makes sure that we do not miss some query patterns
already supported.

Reported-by: Andreas Karlsson
Author: Michael Paquier
Reviewed-by: Andreas Karlsson
Discussion: https://postgr.es/m/20190206091817.GB14980@paquier.xyz

src/test/regress/expected/prepare.out

@@ -145,6 +145,13 @@ SELECT * FROM q5_prep_results;
     9961 |    2058 |   1 |    1 |   1 |      1 |      61 |      961 |        1961 |      4961 |     9961 | 122 |  123 | DTAAAA   | EBDAAA   | OOOOxx
 (16 rows)
 
+CREATE TEMPORARY TABLE q5_prep_nodata AS EXECUTE q5(200, 'DTAAAA')
+    WITH NO DATA;
+SELECT * FROM q5_prep_nodata;
+ unique1 | unique2 | two | four | ten | twenty | hundred | thousand | twothousand | fivethous | tenthous | odd | even | stringu1 | stringu2 | string4 
+---------+---------+-----+------+-----+--------+---------+----------+-------------+-----------+----------+-----+------+----------+----------+---------
+(0 rows)
+
 -- unknown or unspecified parameter types: should succeed
 PREPARE q6 AS
     SELECT * FROM tenk1 WHERE unique1 = $1 AND stringu1 = $2;

src/test/regress/expected/select_into.out

@@ -112,14 +112,15 @@ SELECT * FROM created_table;
  4567890123456789 | -4567890123456789
 (5 rows)
 
--- Try EXPLAIN ANALYZE SELECT INTO, but hide the output since it won't
--- be stable.
+-- Try EXPLAIN ANALYZE SELECT INTO and EXPLAIN ANALYZE CREATE TABLE AS
+-- WITH NO DATA, but hide the outputs since they won't be stable.
 DO $$
 BEGIN
 	EXECUTE 'EXPLAIN ANALYZE SELECT * INTO TABLE easi FROM int8_tbl';
+	EXECUTE 'EXPLAIN ANALYZE CREATE TABLE easi2 AS SELECT * FROM int8_tbl WITH NO DATA';
 END$$;
 DROP TABLE created_table;
-DROP TABLE easi;
+DROP TABLE easi, easi2;
 --
 -- Disallowed uses of SELECT ... INTO.  All should fail
 --

src/test/regress/sql/prepare.sql

@@ -61,6 +61,9 @@ PREPARE q5(int, text) AS
 	ORDER BY unique1;
 CREATE TEMPORARY TABLE q5_prep_results AS EXECUTE q5(200, 'DTAAAA');
 SELECT * FROM q5_prep_results;
+CREATE TEMPORARY TABLE q5_prep_nodata AS EXECUTE q5(200, 'DTAAAA')
+    WITH NO DATA;
+SELECT * FROM q5_prep_nodata;
 
 -- unknown or unspecified parameter types: should succeed
 PREPARE q6 AS

src/test/regress/sql/select_into.sql

@@ -85,15 +85,16 @@ SELECT make_table();
 
 SELECT * FROM created_table;
 
--- Try EXPLAIN ANALYZE SELECT INTO, but hide the output since it won't
--- be stable.
+-- Try EXPLAIN ANALYZE SELECT INTO and EXPLAIN ANALYZE CREATE TABLE AS
+-- WITH NO DATA, but hide the outputs since they won't be stable.
 DO $$
 BEGIN
 	EXECUTE 'EXPLAIN ANALYZE SELECT * INTO TABLE easi FROM int8_tbl';
+	EXECUTE 'EXPLAIN ANALYZE CREATE TABLE easi2 AS SELECT * FROM int8_tbl WITH NO DATA';
 END$$;
 
 DROP TABLE created_table;
-DROP TABLE easi;
+DROP TABLE easi, easi2;
 
 --
 -- Disallowed uses of SELECT ... INTO.  All should fail