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我有以下 mysql 查询，运行大约需要 3 分钟。它确实有 2 个子查询，但表的行数很少。在进行解释时，看起来“使用临时”可能是罪魁祸首。显然，数据库似乎正在为所有三个查询创建一个临时表，如下面的“使用临时”名称中所述。

让我感到困惑的是 MySQL 文档说，使用临时性通常是由 group by 和 order by 引起的，我都没有使用。子查询是否会导致隐含的 group by 或 order by？无论 group by 或 order by 是否都需要导致临时表的子查询？有关如何重组此查询以便 MySQL 可以更有效地处理它的任何建议？MySQL设置中的任何其他调整想法？

mysql> explain
SELECT DISTINCT COMPANY_ID, COMPANY_NAME
  FROM COMPANY
 WHERE ID IN (SELECT DISTINCT ID FROM CAMPAIGN WHERE CAMPAIGN_ID IN (SELECT
              DISTINCT CAMPAIGN_ID FROM AD
              WHERE ID=10 AND (AD_STATUS='R' OR AD_STATUS='T'))
              AND (STATUS_CODE='L' OR STATUS_CODE='A' OR STATUS_CODE='C'));

+----+--------------------+----------+------+---------------+------+---------+------+------+------------------------------+
| id | select_type        | table    | type | possible_keys | key  | key_len | ref  | rows | Extra                        |
+----+--------------------+----------+------+---------------+------+---------+------+------+------------------------------+
|  1 | PRIMARY            | COMPANY  | ALL  | NULL          | NULL |    NULL | NULL | 1207 | Using where; Using temporary |
|  2 | DEPENDENT SUBQUERY | CAMPAIGN | ALL  | NULL          | NULL |    NULL | NULL |  880 | Using where; Using temporary |
|  3 | DEPENDENT SUBQUERY | AD       | ALL  | NULL          | NULL |    NULL | NULL |  264 | Using where; Using temporary |
+----+--------------------+----------+------+---------------+------+---------+------+------+------------------------------+

谢谢！菲尔

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1 回答 1

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我不知道您的架构的结构，但我会尝试以下操作：

CREATE INDEX i_company_id ON company(id);   -- should it be a Primary Key?..
CREATE INDEX i_campaign_id ON campaign(id); -- same, PK here?
CREATE INDEX i_ad_id ON ad(id);             -- the same question applies
ANALYZE TABLE company, campaign, ad;

您的查询可以这样简化： 

SELECT DISTINCT c.company_id, c.company_name
  FROM company c
  JOIN campaign cg ON c.id = cg.id
  JOIN ad ON cg.campaign_id = ad.campaign_id
 WHERE ad.id = 10
   AND ad.ad_status IN ('R', 'T')
   AND ad.status_code IN ('L', 'A', 'C');

DISTINCT子查询中的子句对您来说大大减慢了速度，最后一个就足够了。

于 2012-05-01T05:50:11.920 回答