text: SELECT * FROM t FOR READ ONLY;
  SELECT * FROM t 
    FOR UPDATE OF t2, t3 NOWAIT
    FOR KEY SHARE OF t4;
  SELECT * FROM t LIMIT 5 FOR SHARE SKIP LOCKED;
  SELECT * FROM t FOR NO KEY UPDATE LIMIT 10;
  
  SELECT * FROM (SELECT * FROM mytable FOR UPDATE) ss WHERE col1 = 5;