如何优化下面的sql查询？

Question

我在这里做的是获取预订和重复的用户。这里的预订票不能打印两次。如果用户使用该记录打印票证跟踪器表更新。如果用户两次打印相同的票证，则将其标记为重复。这里的子查询是什么，返回一些标记为重复的预留ID。

    SELECT t1.id AS res_id,
       t1.tx_id,
       t1.tx_date,
       t1.bx_date,
       t1.method,
       t1.theater_id,
       t1.showtime_id,
       t1.category_id,
       t1.amount,
       t1.fname,
       t1.status,
       t1.mobile,
       u.username,
       t2.*
FROM `reservation` AS t1
INNER JOIN
  ( SELECT *
   FROM `tracker`
   WHERE reservation_id IN
       ( SELECT reservation_id
        FROM `tracker`
        GROUP BY reservation_id HAVING ( METHOD = 1
                                        AND TYPE = 0
                                        AND COUNT(*) > 1 )
        OR ( METHOD = 1
            AND TYPE = 1
            AND COUNT(*) > 1 )
        OR ( METHOD = 2
            AND TYPE = 2
            AND COUNT(*) > 0 )
        OR ( METHOD = 3
            AND TYPE = 0
            AND COUNT(*) > 0 )
        OR ( METHOD = 3
            AND TYPE = 1
            AND COUNT(*) > 1 )
        OR ( METHOD = 3
            AND TYPE = 3
            AND COUNT(*) > 0 )) ) AS t2 ON t1.id = t2.reservation_id
INNER JOIN `users` AS u ON u.id = t2.user_id
WHERE t2.resolved = 0
  AND t2.duplicate = 1
ORDER BY t2.issue_date DESC, t1.id DESC

以上查询的EXPLAIN命令。

我该怎么办？如果我索引我应该使用哪些键？如何确定要索引的键？我知道子查询减慢了我应该遵循哪些程序来消除缓慢？

Answer 1

在MySQL中，exists子查询通常比in子查询更快。你可以试试：

SELECT t1.id AS res_id, t1.tx_id, t1.tx_date, t1.bx_date,t1.method, t1.theater_id, t1.showtime_id,
       t1.category_id, t1.amount, t1.fname, t1.status, t1.mobile, u.username, t2.*
FROM `reservation` t1 INNER JOIN
     (SELECT *
      FROM `tracker` t
      WHERE EXISTS (SELECT 1
                    FROM `tracker` t3
                    where t3.reservation_id = t.reservation_id
                    GROUP BY reservation_id
                    HAVING (METHOD = 1 AND TYPE = 0 AND COUNT(*) > 1) OR
                           (METHOD = 1 AND TYPE = 1 AND COUNT(*) > 1) OR
                           (METHOD = 2 AND TYPE = 2 AND COUNT(*) > 0) OR
                           (METHOD = 3 AND TYPE = 0 AND COUNT(*) > 0) OR
                           (METHOD = 3 AND TYPE = 1 AND COUNT(*) > 1) OR
                           (METHOD = 3 AND TYPE = 3 AND COUNT(*) > 0)
                   )
     ) t2
     ON t1.id = t2.reservation_id INNER JOIN
     `users` AS u ON u.id = t2.user_id
WHERE t2.resolved = 0 AND t2.duplicate = 1
ORDER BY t2.issue_date DESC, t1.id DESC

我注意到子查询在having子句中使用了隐藏列。它可能没有做你期望的。通常情况下，查询会在method子句中包含type和group by，或者包含max(Method)等表达式。