PostgreSQL:

CREATE RULE

Topic

CREATE [ OR REPLACE ] RULE name AS ON event
TO table_name [ WHERE condition ]
DO [ ALSO | INSTEAD ] { NOTHING | command | ( command ; command ... ) }

Example

CREATE RULE "_RETURN" AS
ON SELECT TO t1
DO INSTEAD
SELECT * FROM t2;

CREATE RULE "_RETURN" AS
ON SELECT TO t2
DO INSTEAD
SELECT * FROM t1;

SELECT * FROM t1;

CREATE RULE notify_me AS ON UPDATE TO mytable DO ALSO
NOTIFY mytable;

UPDATE mytable SET name = 'foo' WHERE id = 42;

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