[MySQL View]最有意思的视图view优化过程，从30分钟到0.08秒
开发人员写了一个view，select要30分钟，让我优化下，view如下：CREATE ALGORITHM=UNDEFINED SQL SECURITY DEFINER VIEW view_offer_label AS
SELECT ol.OFFER_ID AS OFFER_ID,ol.EFFECTIVE_DATE AS EFFECTIVE_DATE
FROM offer_label ol
WHERE(
ol.ID =
(SELECT ol2.ID
FROM offer_label ol2
WHERE ((ol.OFFER_ID = ol2.OFFER_ID) AND (ol2.LABEL = 'PROD'))
ORDER BY ol2.EFFECTIVE_DATE DESC,ol2.ID DESC LIMIT 1
)
)
开发人员select一下需要30多分钟：
21068 rows in set (1987.08 sec)
先解析一下：
mysql> explain SELECT `ol`.`OFFER_ID` AS `OFFER_ID`,`ol`.`EFFECTIVE_DATE` AS `EFFECTIVE_DATE`
-> FROM `offer_label` `ol`
-> WHERE (`ol`.`ID` =
-> (SELECT `ol2`.`ID`
->FROM `offer_label` `ol2`
->WHERE ((`ol`.`OFFER_ID` = `ol2`.`OFFER_ID`) AND (`ol2`.`LABEL` = 'PROD'))
->ORDER BY `ol2`.`EFFECTIVE_DATE` DESC,`ol2`.`ID` DESC LIMIT 1));
+----+--------------------+-------+-------+------------------------------------+-------------------+---------+---------------------------+--------+------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows| Extra |
+----+--------------------+-------+-------+------------------------------------+-------------------+---------+---------------------------+--------+------------------------------------------+
| 1 | PRIMARY | ol| index | NULL | offer_label_index | 1542| NULL | 143299 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | ol2| ref| OFFER_LABEL_FKEY,offer_label_index | offer_label_index | 1534| const,catalog.ol.OFFER_ID | 1 | Using where; Using index; Using filesort |
+----+--------------------+-------+-------+------------------------------------+-------------------+---------+---------------------------+--------+------------------------------------------+
2 rows in set (0.00 sec)
看到有 Using filesort，要优化where后面的子判断，优化如下：
select max(ol2.ID)
from offer_label ol2
where ol2.LABEL = 'PROD'
group by ol2.OFFER_ID
order by ol2.EFFECTIVE_DATE DESC,ol2.ID DESC;
mysql> explainselect max(ol2.ID)
->from offer_label ol2
->where ol2.LABEL = 'PROD'
->group by ol2.OFFER_ID
->order by ol2.EFFECTIVE_DATE DESC,ol2.ID DESC;
+----+-------------+-------+------+-------------------+-------------------+---------+-------+-------+-----------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref| rows | Extra |
+----+-------------+-------+------+-------------------+-------------------+---------+-------+-------+-----------------------------------------------------------+
| 1 | SIMPLE | ol2| ref | offer_label_index | offer_label_index | 767 | const | 71649 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+-------+------+-------------------+-------------------+---------+-------+-------+-----------------------------------------------------------+
1 row in set (0.00 sec)
有些不对劲，再仔细看了view的结构，恍然大悟：
优化成如下样子：
CREATE ALGORITHM=UNDEFINED SQL SECURITY DEFINER VIEW view_offer_label AS
SELECT ol2.OFFER_ID, max(EFFECTIVE_DATE) EFFECTIVE_DATE
FROM offer_label ol2
WHERE ol2.LABEL = 'PROD'
group by ol2.OFFER_ID ;
执行结果为：
21068 rows in set (0.08 sec)
不到0.08秒，数据完全正确。
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