[Maria-developers] MDEV-25080 Allow pushdown of queries involving UNIONs in outer select to foreign engines

Hello! The implementation for MDEV-25080 is ready and pushed to the *preview-10.11-mdev-25080-union-pushdown *branch. The FederatedX storage engine is adjusted accordingly. The example of how it works can be found at *mysql-test/federated/federatedx_create_handlers.test:* --echo # Pushdown of the whole UNION SELECT * from federated.t1 UNION SELECT * from federated.t2; EXPLAIN SELECT * from federated.t1 UNION SELECT * from federated.t2; --echo # Pushdown of a part of the UNION SELECT * from federated.t1 UNION SELECT * from t3; EXPLAIN SELECT * from federated.t1 UNION SELECT * from t3; -- Best regards, ------------------------- *Oleg Smirnov* Sr. Software Engineer MariaDB Server Team