<lock_statement> ::=
  LOCK [(WAIT)|(NOWAIT)] <lock_spec> IN SHARE MODE
| LOCK [(WAIT)|(NOWAIT)] <lock_spec> IN EXCLUSIVE MODE
| LOCK [(WAIT)|(NOWAIT)] <row_spec>... OPTIMISTIC
| LOCK [(WAIT)|(NOWAIT)] <lock_spec> IN SHARE MODE <lock_spec> IN EXCLUSIVE MODE