Question

以下是我能够获得所需结果的MySQl查询

但有什么方法可以优化查询

SELECT users.*,
    (SELECT country_name FROM country WHERE country_code = users.country_code)
        AS country_name,
    (SELECT zone_name FROM timezone WHERE timezone_id = users.timezone_id)
        AS zone_name,
    (SELECT GROUP_CONCAT(list_name)
     FROM list LEFT JOIN user_list ON user_list.list_id = list.list_id
     WHERE user_list.user_id = users.user_id AND user_list.status = "active")
        AS groups,
    (SELECT GROUP_CONCAT(promotion_name)
     FROM promotion LEFT JOIN promotion_user ON promotion_user.promotion_id = promotion.promotion_id
     WHERE promotion_user.user_id = users.user_id AND promotion_user.status = "active")
         AS promotions,
    (SELECT GROUP_CONCAT(full_name)
     FROM users u LEFT JOIN promotion_user ON promotion_user.promotor_id = u.user_id
     WHERE promotion_user.user_id = users.user_id AND promotion_user.status = "active")
         AS promotors
FROM users WHERE client_id = '2' AND status != 'deleted'
ORDER BY user_id desc
LIMIT 50 OFFSET 0

解释输出

                                                possible        key   
id  select_type         table           type    _keys   key     _len    ref     rows    Extra

1   PRIMARY             users           index   NULL    PRIMARY 4       NULL    1045612 Using where
6   DEPENDENT SUBQUERY  promotion_user  ALL     NULL    NULL    NULL    NULL    16159   Using where
6   DEPENDENT SUBQUERY  u               eq_ref  PRIMARY PRIMARY 4       [1]     1       NULL
5   DEPENDENT SUBQUERY  promotion_user  ALL     NULL    NULL    NULL    NULL    16895   Using where
5   DEPENDENT SUBQUERY  promotion       ALL     PRIMARY NULL    NULL    NULL    4       Using where; Using join buffer (Block Nested Loop)
4   DEPENDENT SUBQUERY  list            ALL     PRIMARY NULL    NULL    NULL    1592    NULL
4   DEPENDENT SUBQUERY  user_list       ALL     NULL    NULL    NULL    NULL    159852  Using where; Using join buffer (Block Nested Loop)
3   DEPENDENT SUBQUERY  timezone        eq_ref  PRIMARY PRIMARY 4       [2]     1       NULL          
2   DEPENDENT SUBQUERY  country         ALL     NULL    NULL    NULL    NULL    239     Using where

                                                                        [1] test.promotion_user.promoter_id
                                                                        [2] test.promotion_user.promoter_id

Answer 1

我会尝试使用非相关的子查询。但是，由于您只是为单个用户带回细节（因此可能是单行），这可能没有帮助。除了可能消除一个子查询。

像这样的东西（未经测试，没有数据定义或数据示例）

SELECT `users`.*,
    country.country_name,
    timezone.zone_name,
    sub_groups.groups,
    sub_promotors.promotions,
    sub_promotors.promotors
FROM `users`
INNER JOIN country
ON country.country_code = users.country_code
INNER JOIN timezone
ON timezone.timezone_id = users.timezone_id
INNER JOIN 
(
    SELECT promotion_user.user_id, GROUP_CONCAT(full_name) AS promotors, GROUP_CONCAT(promotion_name) AS promotions
    FROM users u
    LEFT JOIN promotion_user ON promotion_user.promotor_id = u.user_id
    WHERE promotion_user.status = "active"
    GROUP BY promotion_user.user_id
) AS sub_promotors
ON sub_promotors.user_id = users.user_id
INNER JOIN 
(
    SELECT user_list.user_id, GROUP_CONCAT(list_name) AS groups
    FROM list
    LEFT JOIN user_list ON user_list.list_id = list.list_id
    WHERE user_list.status = "active"
    GROUP BY user_list.user_id
) AS sub_groups
ON sub_groups.user_id = users.user_id
WHERE users.client_id = '2'
AND users.status != 'deleted'
ORDER BY users.user_id 
DESC LIMIT 50 OFFSET 0

相关的子查询有效地强制MySQL为每个返回的行执行一次。将这些更改为连接的非相关子查询意味着可以对所有返回的行执行一次。另一方面，就MySQL中的索引而言，加入子查询的优化程度很低。

如果启动者全名等是唯一的，您可以删除子查询。

使用子查询优化mysql查询

1 个答案: