MDEV-27086 "No database selected" when using UNION of CTEs to define table

This bug concerned only CREATE TABLE statements of the form
  CREATE TABLE <table name> AS <with clause> <union>.
For such a statement not all references to CTE used in <union> were resolved.
As a result a bogus message was reported for the first unresolved reference.
This happened because for such statements the function resolving references
to CTEs LEX::check_cte_dependencies_and_resolve_references() was called
prematurely in the parser.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/r/cte_nonrecursive.result

@@ -2136,4 +2136,30 @@ drop procedure sp1;
 drop function g;
 drop function f;
 drop table t1;
+#
+# MDEV-27086: union using CTEs in CREATE TABLE
+#
+create or replace temporary table tmp as
+with cte1 as (select 1 as a), cte2 as (select 2 as a)
+select * from cte1 union select * from cte2;
+select * from tmp;
+a
+1
+2
+create table t1 as
+with cte1 as (select 1 as a), cte2 as (select 2 as a)
+select * from cte1 union select * from cte2;
+select * from t1;
+a
+1
+2
+insert into t1 values (3);
+create table t2 as
+with cte1 as (select * from t1 where a <2), cte2 as (select * from t1 where a > 2)
+select * from cte1 union select * from cte2;
+select * from t2;
+a
+1
+3
+drop table t1,t2;
 # End of 10.2 tests

mysql-test/t/cte_nonrecursive.test

@@ -1578,4 +1578,27 @@ drop function g;
 drop function f;
 drop table t1;
 
+--echo #
+--echo # MDEV-27086: union using CTEs in CREATE TABLE
+--echo #
+
+create or replace temporary table tmp as
+with cte1 as (select 1 as a), cte2 as (select 2 as a)
+select * from cte1 union select * from cte2;
+select * from tmp;
+
+create table t1 as
+with cte1 as (select 1 as a), cte2 as (select 2 as a)
+select * from cte1 union select * from cte2;
+select * from t1;
+
+insert into t1 values (3);
+
+create table t2 as
+with cte1 as (select * from t1 where a <2), cte2 as (select * from t1 where a > 2)
+select * from cte1 union select * from cte2;
+select * from t2;
+
+drop table t1,t2;
+
 --echo # End of 10.2 tests

sql/sql_yacc.yy

@@ -4869,6 +4869,10 @@ create_like:
 opt_create_select:
           /* empty */ {}
         | opt_duplicate opt_as create_select_query_expression
+          {
+            if (Lex->check_cte_dependencies_and_resolve_references())
+              MYSQL_YYABORT;
+          }
         ;
 
 create_select_query_expression:
@@ -4877,16 +4881,12 @@ create_select_query_expression:
           { 
             Select->set_braces(0);
             Select->set_with_clause($1);
-            if (Lex->check_cte_dependencies_and_resolve_references())
-              MYSQL_YYABORT;
           }
           union_clause
         | opt_with_clause SELECT_SYM create_select_part2 
           create_select_part3_union_not_ready create_select_part4
           {
             Select->set_with_clause($1);
-            if (Lex->check_cte_dependencies_and_resolve_references())
-              MYSQL_YYABORT;
           }
         | '(' create_select_query_specification ')'
         | '(' create_select_query_specification ')'