MySQL：因为统计信息错误引起的sql问题

发现系统以下SQL在S1执行时间3S，但是S2上执行时间0.3S，差距很大，原因为c的子查询执行计划有问题，sql如下

SELECT 
  a.gather_name,
  a.gender,
  c.* 
FROM
  (SELECT 
    n.gather_name,
    n.gather_ids,
    n.gender 
  FROM
     n 
  WHERE n.id = 35) a 
  JOIN 
    (SELECT DISTINCT 
      d.* 
    FROM
       d 
      JOIN  e 
        ON d.`category_id` = e.`category_id` 
      JOIN  p 
        ON p.`goods_id` = e.`goods_id` 
      JOIN  s 
        ON s.`product_id` = p.`product_id` 
        AND s.`stock` - s.`fix_stock` > 0 
        AND s.status = 1 
        AND e.gender IN (0, 1, 2) 
    ORDER BY sort DESC) c 
    ON INSTR(
      a.gather_ids,
      CONCAT(',', c.category_id, ',')
    ) > 0 
ORDER BY c.sort ASC 

S1上c子查询的执行计划：

mysql> explain SELECT DISTINCT 
    ->       d.* 
    ->     FROM
    ->        d 
    ->       JOIN  e 
    ->         ON d.`category_id` = e.`category_id` 
    ->       JOIN  p 
    ->         ON p.`goods_id` = e.`goods_id` 
    ->       JOIN  s 
    ->         ON s.`product_id` = p.`product_id` 
    ->         AND s.`stock` - s.`fix_stock` > 0 
    ->         AND s.status = 1 
    ->         AND e.gender IN (0, 1, 2) 
    ->     ORDER BY sort DESC;
+----+-------------+-------+--------+-----------------------------------+------------+---------+-----------------------+--------+----------------------------------------------+
| id | select_type | table | type   | possible_keys                     | key        | key_len | ref                   | rows   | Extra                                        |
+----+-------------+-------+--------+-----------------------------------+------------+---------+-----------------------+--------+----------------------------------------------+
|  1 | SIMPLE      | e     | ALL    | PRIMARY,category_id,goods_id      | NULL       | NULL    | NULL                  | 138326 | Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | d     | eq_ref | PRIMARY,category_id,category_id_2 | PRIMARY    | 4       | shop_zp.e.category_id |      1 |                                              |
|  1 | SIMPLE      | p     | ref    | PRIMARY,goods_id,product_id       | goods_id   | 4       | shop_zp.e.goods_id    |      1 | Using index; Distinct                        |
|  1 | SIMPLE      | s     | ref    | product_id                        | product_id | 4       | shop_zp.p.product_id  |      1 | Using where; Distinct                        |
+----+-------------+-------+--------+-----------------------------------+------------+---------+-----------------------+--------+----------------------------------------------+
执行时间：307 rows in set (2.96 sec)

加上hint，强制执行顺序的执行计划：
mysql> explain SELECT DISTINCT 
    ->       d.* 
    ->     FROM
    ->        d 
    ->       STRAIGHT_JOIN  e 
    ->         ON d.`category_id` = e.`category_id` 
    ->       JOIN  p 
    ->         ON p.`goods_id` = e.`goods_id` 
    ->       JOIN  s 
    ->         ON s.`product_id` = p.`product_id` 
    ->         AND s.`stock` - s.`fix_stock` > 0 
    ->         AND s.status = 1 
    ->         AND e.gender IN (0, 1, 2) 
    ->     ORDER BY sort DESC;
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
| id | select_type | table | type | possible_keys                     | key         | key_len | ref                   | rows | Extra                           |
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
|  1 | SIMPLE      | d     | ALL  | PRIMARY,category_id,category_id_2 | NULL        | NULL    | NULL                  |  895 | Using temporary; Using filesort |
|  1 | SIMPLE      | e     | ref  | PRIMARY,category_id,goods_id      | category_id | 4       | shop_zp.d.category_id |  289 | Using where; Distinct           |
|  1 | SIMPLE      | p     | ref  | PRIMARY,goods_id,product_id       | goods_id    | 4       | shop_zp.e.goods_id    |    1 | Using index; Distinct           |
|  1 | SIMPLE      | s     | ref  | product_id                        | product_id  | 4       | shop_zp.p.product_id  |    1 | Using where; Distinct           |
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
执行时间：307 rows in set (0.25 sec)

查询`information_schema`.`TABLES`，information_schema.statistics发现以下两表和实际数据有些差距

mysql> ANALYZE TABLE e;
+------------------+---------+----------+----------+
| Table            | Op      | Msg_type | Msg_text |
+------------------+---------+----------+----------+
| shop_zp.e        | analyze | status   | OK       |
+------------------+---------+----------+----------+
1 row in set (0.00 sec)

mysql> ANALYZE TABLE p;
+---------------------+---------+----------+----------+
| Table               | Op      | Msg_type | Msg_text |
+---------------------+---------+----------+----------+
| shop_zp.p           | analyze | status   | OK       |
+---------------------+---------+----------+----------+
1 row in set (0.01 sec)

分析后，S1的执行计划：

mysql> explain SELECT DISTINCT 
    ->       d.* 
    ->     FROM
    ->        d 
    ->       JOIN  e 
    ->         ON d.`category_id` = e.`category_id` 
    ->       JOIN  p 
    ->         ON p.`goods_id` = e.`goods_id` 
    ->       JOIN  s 
    ->         ON s.`product_id` = p.`product_id` 
    ->         AND s.`stock` - s.`fix_stock` > 0 
    ->         AND s.status = 1 
    ->         AND e.gender IN (0, 1, 2) 
    ->     ORDER BY sort DESC;
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
| id | select_type | table | type | possible_keys                     | key         | key_len | ref                   | rows | Extra                           |
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
|  1 | SIMPLE      | d     | ALL  | PRIMARY,category_id,category_id_2 | NULL        | NULL    | NULL                  |  634 | Using temporary; Using filesort |
|  1 | SIMPLE      | e     | ref  | PRIMARY,category_id,goods_id      | category_id | 4       | shop_zp.d.category_id |  206 | Using where; Distinct           |
|  1 | SIMPLE      | p     | ref  | PRIMARY,goods_id,product_id       | goods_id    | 4       | shop_zp.e.goods_id    |    1 | Using index; Distinct           |
|  1 | SIMPLE      | s     | ref  | product_id                        | product_id  | 4       | shop_zp.p.product_id  |    1 | Using where; Distinct           |
+----+-------------+-------+------+-----------------------------------+-------------+---------+-----------------------+------+---------------------------------+
此时该SQL在S1执行时间正常。
不过依然得吐槽，MySQL的统计信息和真实数据差距还是挺大！！
对MySQL统计信息了解还是不深！！待加强！！