DROP TABLE IF EXISTS t1, t2;

CREATE TABLE t1 (a INT);

CREATE TABLE t2 (b INT);

# This query works of course

SELECT * FROM t1 WHERE EXISTS ( SELECT * FROM t2 WHERE b = a );

# But this does not

SELECT * FROM t1 WHERE EXISTS ( WITH cte AS ( SELECT * FROM t2 WHERE b = a ) SELECT * FROM cte );

MariaDB [test]> SELECT * FROM t1 WHERE EXISTS ( SELECT * FROM t2 WHERE b = a );

Empty set (0.01 sec)

MariaDB [test]> SELECT * FROM t1 WHERE EXISTS ( WITH cte AS ( SELECT * FROM t2 WHERE b = a ) SELECT * FROM cte );

ERROR 1054 (42S22): Unknown column 'a' in 'where clause'