SELECT count(1) FROM APPLY t WHERE EXISTS ( SELECT r.APPLY_ID FROM RECORD r WHERE t.APPLY_ID = r.APPLY_ID );
SELECT count(1) FROM APPLY t WHERE EXISTS ( SELECT max(r.FINISH_TIME) FROM RECORD r WHERE t.APPLY_ID = r.APPLY_ID );
mysql> create table t3(id int,t datetime); Query OK, 0 rows affected (0.44 sec) mysql> insert into t3 values(1,'20160812'); Query OK, 1 row affected (0.16 sec) mysql> select 1 from dual where exists (select id from t3 where id=2); Empty set (0.15 sec) mysql> select 1 from dual where exists (select max(id) from t3 where id=2); +---+ | 1 | +---+ | 1 |
mysql> EXPLAIN EXTENDED select 1 from dual where exists (select id from t3 where id=2); +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ | 1 | PRIMARY | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE | | 2 | SUBQUERY | t3 | NULL | ALL | NULL | NULL | NULL | NULL | 1 | 100.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+ 2 rows in set, 2 warnings (0.00 sec) mysql> show warnings; +---------+------+-------------------------------------------------------------------+ | Level | Code | Message | +---------+------+-------------------------------------------------------------------+ | Warning | 1681 | 'EXTENDED' is deprecated and will be removed in a future release. | | Note | 1003 | /* select#1 */ select 1 AS `1` from DUAL where 0 | +---------+------+-------------------------------------------------------------------+
mysql> EXPLAIN EXTENDED select 1 from dual where exists (select max(id) from t3 where id=2); +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ | 1 | PRIMARY | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used | | 2 | SUBQUERY | t3 | NULL | ALL | NULL | NULL | NULL | NULL | 1 | 100.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ 2 rows in set, 2 warnings (0.00 sec) mysql> show warnings; +---------+------+-------------------------------------------------------------------+ | Level | Code | Message | +---------+------+-------------------------------------------------------------------+ | Warning | 1681 | 'EXTENDED' is deprecated and will be removed in a future release. | | Note | 1003 | /* select#1 */ select 1 AS `1` from DUAL where 1 | +---------+------+-------------------------------------------------------------------+ 2 rows in set (0.00 sec)
mysql> select 1 from dual where exists (select abs(id) from t3 where id=2); Empty set (0.07 sec) mysql> select 1 from dual where exists (select floor(id) from t3 where id=2); Empty set (0.00 sec)
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