Mysql Sql查询优化与调试

我正在尝试优化mysql数据库中的sql查询。尝试了不同的重写方法，添加/删除索引，但似乎没有任何东西可以减少负载。也许我错过了什么。 查询：

持续时间：2.01秒-2.20秒 优化查询：

    select co.country_name as state, ci.city_name as city, ci.city_id, ci.country_id, count(l.id) as num from 
(select ci1.city_name, ci1.city_id, ci1.country_id from cities ci1 
where ci1.main=1) as ci 
INNER JOIN countries co ON (ci.country_id = co.country_id) 
INNER JOIN dancers l ON (l.city_id = ci.city_id AND l.closed = 0 AND l.approved = 1 ) GROUP BY ci.city_id ORDER BY city

持续时间：0.82秒-0.90秒

但是我觉得这个查询可以被优化得更多，但是没有得到如何优化它的想法。有三张桌子

Table 1 : countries ( country_id, country_name)
Table 2 : cities ( city_id, city_name, main, country_id)
Table 3 : dancers ( id, country_id, city_id, closed, approved) 

我正在尝试获取main=1的所有城市，并为每个城市统计加入国家的城市的所有配置文件，以获得国家名称

欢迎提出任何意见，谢谢

稍后编辑：-第一个查询解释

+----+-------------+-------+-------------+---------------------------------------------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
| id | select_type | table |    type     |                            possible_keys                            |       key       | key_len |       ref        | rows  |                                     Extra                                      |
+----+-------------+-------+-------------+---------------------------------------------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
|  1 | SIMPLE      | l     | index_merge | city_id,closed,approved,city_id_2                                   | closed,approved |     1,2 | NULL             | 75340 | Using intersect(closed,approved); Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | ci    | eq_ref      | PRIMARY,state_id_2,state_id,city_name,lat,city_name_shorter,city_id | PRIMARY         |       4 | db.l.city_id     |     1 | Using where                                                                    |
|  1 | SIMPLE      | co    | eq_ref      | PRIMARY                                                             | PRIMARY         |       4 | db.ci.country_id |     1 | Using where                                                                    |
+----+-------------+-------+-------------+---------------------------------------------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+

第二个问题解释：

+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
| id | select_type |   table    | type |           possible_keys           |     key     | key_len |       ref        | rows  |               Extra                |
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
|  1 | PRIMARY     | co         | ALL  | PRIMARY                           | NULL        | NULL    | NULL             |    51 | Using temporary; Using filesort    |
|  1 | PRIMARY     | <derived2> | ref  | <auto_key1>                       | <auto_key1> | 4       | db.co.country_id |   176 | Using where                        |
|  1 | PRIMARY     | l          | ref  | city_id,closed,approved,city_id_2 | city_id_2   | 4       | ci.city_id       |    44 | Using index condition; Using where |
|  2 | DERIVED     | ci1        | ALL  | NULL                              | NULL        | NULL    | NULL             | 11765 | Using where                        |
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+

+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
| id | select_type |   table    |    type     |           possible_keys           |       key       | key_len |       ref        | rows  |                                     Extra                                      |
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
|  1 | PRIMARY     | co         | ALL         | PRIMARY                           | NULL            | NULL    | NULL             |    51 | NULL                                                                           |
|  1 | PRIMARY     | <derived2> | ref         | <auto_key0>                       | <auto_key0>     | 4       | db.co.country_id |   565 | Using where                                                                    |
|  2 | DERIVED     | l          | index_merge | city_id,closed,approved,city_id_2 | closed,approved | 1,2     | NULL             | 75341 | Using intersect(closed,approved); Using where; Using temporary; Using filesort |
|  2 | DERIVED     | ci1        | eq_ref      | PRIMARY,state_id_2,city_id        | PRIMARY         | 4       | db.l.city_id     |     1 | Using where                                                                    |
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+

+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
|id |选择|类型|类型|可能的|键|键|列|参考|行|额外|
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
|1 | PRIMARY | co | ALL | PRIMARY | NULL | NULL | NULL | 51 |使用临时命令；使用文件排序|
|1 |主要| |参考| | | | 4 | db.co.country|u id | 176 |使用where|
|1 |主要| l |参考|城市id，关闭，批准，城市id | 2 |城市id | 2 | 4 | ci.city | id | 44 |使用索引条件；在哪里使用|
|2 |导出的| ci1 | ALL | NULL | NULL | NULL | NULL | 11765 |使用where|
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+

@已由\u使用\u查询解释：

+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
| id | select_type |   table    | type |           possible_keys           |     key     | key_len |       ref        | rows  |               Extra                |
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+
|  1 | PRIMARY     | co         | ALL  | PRIMARY                           | NULL        | NULL    | NULL             |    51 | Using temporary; Using filesort    |
|  1 | PRIMARY     | <derived2> | ref  | <auto_key1>                       | <auto_key1> | 4       | db.co.country_id |   176 | Using where                        |
|  1 | PRIMARY     | l          | ref  | city_id,closed,approved,city_id_2 | city_id_2   | 4       | ci.city_id       |    44 | Using index condition; Using where |
|  2 | DERIVED     | ci1        | ALL  | NULL                              | NULL        | NULL    | NULL             | 11765 | Using where                        |
+----+-------------+------------+------+-----------------------------------+-------------+---------+------------------+-------+------------------------------------+

+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
| id | select_type |   table    |    type     |           possible_keys           |       key       | key_len |       ref        | rows  |                                     Extra                                      |
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
|  1 | PRIMARY     | co         | ALL         | PRIMARY                           | NULL            | NULL    | NULL             |    51 | NULL                                                                           |
|  1 | PRIMARY     | <derived2> | ref         | <auto_key0>                       | <auto_key0>     | 4       | db.co.country_id |   565 | Using where                                                                    |
|  2 | DERIVED     | l          | index_merge | city_id,closed,approved,city_id_2 | closed,approved | 1,2     | NULL             | 75341 | Using intersect(closed,approved); Using where; Using temporary; Using filesort |
|  2 | DERIVED     | ci1        | eq_ref      | PRIMARY,state_id_2,city_id        | PRIMARY         | 4       | db.l.city_id     |     1 | Using where                                                                    |
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+

+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
|id |选择|类型|类型|可能的|键|键|列|参考|行|额外|
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+
|1 | PRIMARY | co | ALL | PRIMARY | NULL | NULL | NULL | 51 | NULL|
|1 |主要| |参考| | | | 4 | db.co.country|u id | 565 |使用where|
|2 |派生| l |索引|合并|城市| id，关闭，批准，城市| id | 2 |关闭，批准| 1,2 |空| 75341 |使用intersect（关闭，批准）；在何处使用；使用临时设备；使用文件排序|
|2 |派生| ci1 |等式|参考|主要，州| id | 2，城市|主要| 4 | db.l.city | id | 1 |使用其中|
+----+-------------+------------+-------------+-----------------------------------+-----------------+---------+------------------+-------+--------------------------------------------------------------------------------+

我建议您尝试以下方法：

SELECT
      co.country_name AS state
    , ci.city_name    AS city
    , ci.city_id
    , ci.country_id
    , ci.num
FROM (
      SELECT
            ci1.city_id
          , ci1.city_name
          , ci1.country_id
          , COUNT(l.id) AS num
      FROM cities ci1
      INNER JOIN dancers l ON l.city_id = ci1.city_id
            AND l.closed = 0
            AND l.approved = 1
      WHERE ci1.main = 1
      GROUP BY
            ci1.city_id
          , ci1.city_name
          , ci1.country_id
      ) AS ci
INNER JOIN countries co ON ci.country_id = co.country_id
;

如果需要，您可以提供解释计划输出以供进一步分析。当优化时，知道存在哪些指标，并让他解释计划，是最基本的

此外，MySQL不允许使用非标准的GROUPBY语法（在GROUPBY子句下只包含select列表中的一列或部分列）。

---

在MySQL的最新版本中，GROUPBY的默认行为已更改为SQL标准语法（其中select列表中的所有“非聚合”列必须包含在GROUPBY子句下）。虽然您现有的查询使用非标准的group by语法，但此处提供的查询不符合要求。

请包含解释计划输出（作为文本）我用解释“作为文本”编辑了第一篇文章，您更有可能让人们阅读材料，因为它是格式化文本…认为图片更有用，添加了格式化文本。

city\u id，closed，approved

的索引（按列顺序C，on dancers）似乎会有所帮助。您是否获得此查询变体的解释计划？在主体中也添加了查询解释