Fixed the bug mdev-12440.

When a CTE referring to another CTE from the same with clause
was used twice then the server could not find the second CTE and
reported a bogus error message.
This happened because for any unit that was created as a clone of
a CTE specification the pointer to the WITH clause that owned this CTE
was not set.

mysql-test/r/cte_nonrecursive.result

@@ -961,3 +961,26 @@ show create view v1;
 View	Create View	character_set_client	collation_connection
 v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS with alias1 as (select 1 AS `one`), alias2 as (select 2 AS `two`)select `alias1`.`one` AS `one`,`alias2`.`two` AS `two` from (`alias1` join `alias2`)	latin1	latin1_swedish_ci
 drop view v1;
+#
+# MDEV-12440: the same CTE table is used in twice
+#
+create table t1 (a int, b  varchar(32));
+insert into t1 values
+(4,'aaaa' ), (7,'bb'), (1,'ccc'), (4,'dd');
+# cte2 is used in the main query and in the spec for ct3
+with
+cte1 as (select * from t1 where  b >= 'c'),
+cte2 as (select * from cte1 where a < 7),
+cte3 as (select * from cte2 where a > 1)
+select * from cte2, cte3 where cte2.a = cte3.a;
+a	b	a	b
+4	dd	4	dd
+# cte2 is used twice in the spec for ct3
+with
+cte1 as (select * from t1 where  b >= 'b'),
+cte2 as (select * from cte1 where b > 'c'),
+cte3 as (select * from cte2 where a > 1 union select * from cte2 where a > 1)
+select * from cte3;
+a	b
+4	dd
+drop table t1;

mysql-test/t/cte_nonrecursive.test

@@ -642,3 +642,27 @@ select * from v1;
 show create view v1;
 
 drop view v1;
+
+--echo #
+--echo # MDEV-12440: the same CTE table is used in twice
+--echo #
+
+create table t1 (a int, b  varchar(32));
+insert into t1 values
+  (4,'aaaa' ), (7,'bb'), (1,'ccc'), (4,'dd');  
+
+--echo # cte2 is used in the main query and in the spec for ct3
+with
+cte1 as (select * from t1 where  b >= 'c'),
+cte2 as (select * from cte1 where a < 7),
+cte3 as (select * from cte2 where a > 1)
+select * from cte2, cte3 where cte2.a = cte3.a;
+
+--echo # cte2 is used twice in the spec for ct3
+with
+cte1 as (select * from t1 where  b >= 'b'),
+cte2 as (select * from cte1 where b > 'c'),
+cte3 as (select * from cte2 where a > 1 union select * from cte2 where a > 1)
+select * from cte3;
+
+drop table t1;
\ No newline at end of file

sql/sql_cte.cc

@@ -780,6 +780,7 @@ st_select_lex_unit *With_element::clone_parsed_spec(THD *thd,
     with_table->next_global= spec_tables;
   }
   res= &lex->unit;
+  res->set_with_clause(owner);
   
   lex->unit.include_down(with_table->select_lex);
   lex->unit.set_slave(with_select);