MySQL查询缓存，复杂的SQL查询

Question

接下来的问题让我头疼。

我已经将MySQL服务器设置为使用“查询缓存”。

set global query_cache_size = 10000000;

看来我的查询缓存有效，因为

SHOW STATUS LIKE 'Qcache%';  

如下

+-------------------------+----------+    
|    Variable_name        | Value    |           
+-------------------------+----------+     
| Qcache_free_blocks      | 1        |
| Qcache_free_memory      | 47223976 |
| Qcache_hits             | 6709     |                                       
| Qcache_inserts          | 2314     |                                    
| Qcache_lowmem_prunes    | 0        |                                  
| Qcache_not_cached       | 365      |                                  
| Qcache_queries_in_cache | 441      |                                   
| Qcache_total_blocks     | 960      |                                     
+-------------------------+----------+ 

但是，无论如何，以下内容（复杂查询，内部选择等）不会被缓存。

始终需要至少0.8秒才能检索此查询的数据。 我如何带mysql将查询结果存储在缓存中 ？

我试着删除内部选择，但这并没有什么区别。

SELECT p.id
   AS
   project_id,
   p.code
   AS project_code,
   p.title
   AS project_title,
   p.start_date
   AS project_start_date,
   p.end_date
   AS project_end_date,
   p.modf
   AS project_modf,
   ( p.budget * (SELECT 1 / r.VALUE
                 FROM   exchange_rates r
                 WHERE  r.class_currency_id = p.class_budget_currency_id) )
   AS
   project_budget,
   (SELECT z.txt
    FROM   sys_labels z
    WHERE  z.id = ps.value_label_id
           AND z.lng = 'en')
   AS project_status,
   (SELECT z.txt
    FROM   sys_labels z
    WHERE  z.id = ps.data_label_id
           AND z.lng = 'en')
   AS project_color,
   GROUP_CONCAT(DISTINCT pt.class_topic_id)
   AS projects_thematic_area_ids,
   u.id
   AS project_owner_id
FROM   projects AS p
   LEFT JOIN projects_thematic_areas AS pt
     ON pt.project_id = p.id
   LEFT JOIN sys_users AS u
     ON u.id = p.owner_uid
   LEFT JOIN class_data s
     ON s.id = p.class_status_id
   LEFT JOIN class_data AS ps
     ON ps.id = s.id
   LEFT JOIN sys_labels AS prdz1
     ON prdz1.id = prd.value_label_id
        AND prdz1.lng = 'en'
   LEFT JOIN sys_labels AS prdz2
     ON prdz2.id = prd.data_label_id
        AND prdz2.lng = 'en'
   LEFT JOIN projects_locations AS pl
     ON pl.project_id = p.id
   LEFT JOIN class_data AS l
     ON l.id = pl.class_location_id
   LEFT JOIN class_data AS r
     ON r._lft <= l._lft
        AND r._rgt >= l._rgt
        AND r._level = 1
        AND r.class_id = 5
   LEFT JOIN class_data AS c
     ON c._lft <= l._lft
        AND c._rgt >= l._rgt
        AND c._level = 2
        AND c.class_id = 10
   LEFT JOIN projects_donors AS pd
     ON pd.project_id = p.id
   LEFT JOIN institutions AS i
     ON pd.inst_id = i.id
   LEFT JOIN class_data AS ic
     ON ic.id = i.class_country_id
   LEFT JOIN projects_deliverables AS d
     ON d.project_id = p.id
WHERE  1 = 1
   AND p.is_del = "f"
   AND p.is_active = "t"
GROUP  BY p.id
ORDER  BY p.modf DESC,
      p.code DESC 

任何帮助感激....

问候

J.

Answer 1

除以前的答案外：即使所选表中有任何更改，即使查询在其中，也不会使用查询缓存。

但是，当您没有从表中选择任何内容时，为什么还要加入这些表呢？ 另外，如果可以加入，您可能不应该子选择任何内容。

这样的选择将完全相同：

SELECT
   p.id AS project_id,
   p.code AS project_code,
   p.title AS project_title,
   p.start_date AS project_start_date,
   p.end_date AS project_end_date,
   p.modf AS project_modf,
   p.budget * (1 / r.VALUE) AS project_budget,
   z1.txt AS project_status,
   z2.txt AS project_color,
   GROUP_CONCAT(DISTINCT pt.class_topic_id) AS projects_thematic_area_ids,
   u.id AS project_owner_id
FROM
   projects AS p
   LEFT JOIN projects_thematic_areas AS pt ON pt.project_id = p.id
   LEFT JOIN sys_users AS u ON u.id = p.owner_uid
   LEFT JOIN exchange_rates AS r ON r.class_currency_id = p.class_budget_currency_id
   LEFT JOIN class_data s ON s.id = p.class_status_id
   LEFT JOIN class_data AS ps ON ps.id = s.id
   LEFT JOIN sys_labels AS z1 ON z1.id = ps.value_label_id AND z1.lng = 'en'
   LEFT JOIN sys_labels AS z2 ON z2.id = ps.data_label_id AND z2.lng = 'en'
WHERE
   1
   AND p.is_del = "f"
   AND p.is_active = "t"
GROUP  BY
   p.id
ORDER  BY
   p.modf DESC,
   p.code DESC 

当然，您在所有外键（字段和组字段）上都有（组合）索引。 考虑为布尔值使用tinyint或枚举字段。 您可能还需要考虑不要选择该GROUP_CONCAT，这样您可能会丢失GROUP BY。 如果您确定该关系存在，则可以使用INNER JOIN而不是LEFT JOIN。

Answer 2

您可以尝试SELECT SQL_CACHE ... FROM ...

Answer 3

您可以尝试一些基本操作：

• 阅读查询缓存文档 ，以确保您了解基础知识并正确设置。
• 理想情况下，隔离MySQL数据库服务器，使其仅运行您提供的命令。 如果无法执行此操作，请尝试在另一台计算机上设置并运行测试。
• 运行一个简单的查询，并查看Qcache_hits和Com_select状态变量，以确定是否命中了查询缓存。
• 尝试复杂的查询并监视相同的值。 如果您的查询没有到达缓存，则尝试查询的较小部分，直到找出导致其无法缓存的原因。 如果要对其进行缓存，则问题可能是由于查询之间的任何表在查询之间进行了更新而导致缓存的副本无效。