如果第一个resutl为false，mysql sleep将无法正常工作

mysql> select * from users where id=0;
Empty set (0.00 sec)

mysql> select * from users where id=0 and sleep(5);
Empty set (0.00 sec)

mysql> select * from users where id=0 and benchmark(1000000,sha1(1));
Empty set (0.39 sec)

mysql> select * from users where id=0 xor sleep(5);
Empty set (1 min 5.02 sec)
mysql> select * from users where id=0;
Empty se