查询条件字段做运算优化

查询条件字段做运算优化

对字段做函数和运算完后无法使用索引。这么做的话，让优化器对字段产生歧义，不知道如何选择索引。因为这时候并没有一个concat(year_id,'-',month_id)这样的字段

mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  concat(year_id,'-',if(month_id<10,'0',''),month_id)='2011-09';

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

| id | select_type | table                          | type | possible_keys | key  | key_len | ref  | rows    | Extra       |

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

|  1 | SIMPLE      | mkt_order_by_month_userid_type | ALL  | NULL          | NULL | NULL    | NULL | 3673176 | Using where |

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

1 row in set (0.00 sec)

mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  concat(year_id,'-',month_id)='2011-09';

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

| id | select_type | table                          | type | possible_keys | key  | key_len | ref  | rows    | Extra       |

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

|  1 | SIMPLE      | mkt_order_by_month_userid_type | ALL  | NULL          | NULL | NULL    | NULL | 3673176 | Using where |

+----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+

1 row in set (0.00 sec)

优化方法，对要传入的值做函数操作

mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  year_id=substring('2011-09',1,4) and month_id = substring('2011-09',6,2);

+----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+

| id | select_type | table                          | type | possible_keys | key     | key_len | ref         | rows   | Extra |

+----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+

|  1 | SIMPLE      | mkt_order_by_month_userid_type | ref  | year_id       | year_id | 8       | const,const | 377128 |       |

+----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+