CREATE TABLE x (id INT) ; INSERT INTO x VALUES (1); INSERT INTO x VALUES (2); INSERT INTO x VALUES (3); INSERT INTO x VALUES (4); mm_testsql=# SELECT * FROM x FOR UPDATE LIMIT 1; id ---- 1 (1 row)Simple enough. Now, in a separate transaction, run the following mm_testsql=# BEGIN ; BEGIN mm_testsql=# DELETE FROM X WHERE id = 1 ; DELETE 1Select for update will now block mm_testsql=# SELECT * FROM x FOR UPDATE LIMIT 1;And finally, commit in the mm_testsql=# COMMIT ; COMMIT mm_testsql=#In the original transaction, the following is returned id ---- (0 rows)