<pre name="code" class="html">mysql> desc AssignClientManager; +-----------------+----------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------+----------+------+-----+---------+----------------+ | sn | int(11) | NO | PRI | NULL | auto_increment | | clientSn | int(11) | NO | MUL | NULL | | | clientManagerSn | int(11) | NO | | NULL | | | status | char(1) | NO | | 1 | | | createdTime | datetime | YES | | NULL | | | updatedTime | datetime | YES | | NULL | | +-----------------+----------+------+-----+---------+----------------+ 6 rows in set (0.00 sec) mysql> show index from AssignClientManager; +---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | AssignClientManager | 0 | PRIMARY | 1 | sn | A | 4934 | NULL | NULL | | BTREE | | | | AssignClientManager | 1 | ACM_IDX1 | 1 | clientSn | A | 4458 | NULL | NULL | | BTREE | | | +---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 2 rows in set (0.00 sec) mysql> explian select sn,clientSn from AssignClientManager; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'explian select sn,clientSn from AssignClientManager' at line 1 mysql> explain select sn,clientSn from AssignClientManager; +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ | 1 | SIMPLE | AssignClientManager | NULL | index | NULL | ACM_IDX1 | 4 | NULL | 4934 | 100.00 | Using index | +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) mysql> explain SELECT COUNT(sn) FROM AssignClientManager where clientSn>5; +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | AssignClientManager | NULL | range | ACM_IDX1 | ACM_IDX1 | 4 | NULL | 4928 | 100.00 | Using where; Using index | +----+-------------+---------------------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> explain select * from AssignClientManager where sn <100 and clientSn <200; +----+-------------+---------------------+------------+-------+------------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------------------+------------+-------+------------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | AssignClientManager | NULL | range | PRIMARY,ACM_IDX1 | PRIMARY | 4 | NULL | 99 | 4.95 | Using where | +----+-------------+---------------------+------------+-------+------------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.01 sec)