带有连接和子查询的 mysql 查询优化

Question

有人可以帮忙吗？来自慢日志 下面的这个查询需要 11 秒才能运行并且它会占用服务器资源。如何重新编写此查询以实现更大的优化？

P.S: 表格已编入索引。

查询：

SELECT SUM(the_val) AS value
FROM
  (SELECT DISTINCT basic_data.id,
                   att2.the_val
   FROM province_create
   INNER JOIN basic_data ON province_create.province = basic_data.province
   INNER JOIN att2 ON att2.church_id = basic_data.id
   WHERE province_create.block = 0
     AND att2.month = 'Feb'
     AND att2.year = '2017'
     AND basic_data.parish = 1
     AND att2.report = 'ATTENDANCE'
     AND province_create.disable = 0 ) t1;

解释报告：

[1] => 数组 ( [0] => 1 [id] => 1 [1] => 初级 [select_type] => 初级 [2] => [表] => [3] => 全部 [类型] => 全部 [4] => [可能的键] => [5] => [关键] => [6] => [key_len] => [7] => [参考] => [8] => 38339 [行] => 38339 [9] => [额外] => )

[2] => Array
    (
        [0] => 2
        [id] => 2
        [1] => DERIVED
        [select_type] => DERIVED
        [2] => province_create
        [table] => province_create
        [3] => ALL
        [type] => ALL
        [4] => kk,province,kkk
        [possible_keys] => kk,province,kkk
        [5] => 
        [key] => 
        [6] => 
        [key_len] => 
        [7] => 
        [ref] => 
        [8] => 261
        [rows] => 261
        [9] => Using where; Using temporary
        [Extra] => Using where; Using temporary
    )

[3] => Array
    (
        [0] => 2
        [id] => 2
        [1] => DERIVED
        [select_type] => DERIVED
        [2] => basic_data
        [table] => basic_data
        [3] => ref
        [type] => ref
        [4] => PRIMARY,kk,kkk,k,parish
        [possible_keys] => PRIMARY,kk,kkk,k,parish
        [5] => kk
        [key] => kk
        [6] => 56
        [key_len] => 56
        [7] => databaseuser.province_create.province
        [ref] => databaseuser.province_create.province
        [8] => 39
        [rows] => 39
        [9] => Using index; Distinct
        [Extra] => Using index; Distinct
    )

[4] => Array
    (
        [0] => 2
        [id] => 2
        [1] => DERIVED
        [select_type] => DERIVED
        [2] => att2
        [table] => att2
        [3] => ref
        [type] => ref
        [4] => indpull,mmm
        [possible_keys] => indpull,mmm
        [5] => mmm
        [key] => mmm
        [6] => 57
        [key_len] => 57
        [7] => databaseuser.basic_data.id
        [ref] => databaseuser.basic_data.id
        [8] => 1
        [rows] => 1
        [9] => Using where; Distinct
        [Extra] => Using where; Distinct
    )

)

Answer 1

首先，让我假设不需要SELECT DISTINCT。那么查询可以写成：

SELECT SUM(a.the_val)
FROM province_create pc INNER JOIN
     basic_data bd
     ON pc.province = bd.province INNER JOIN
     att2 a
     ON a.church_id = bd.id
WHERE pc.block = 0 AND
      a.month = 'Feb' AND
      a.year = '2017' AND
      bd.parish = 1 AND
      a.report = 'ATTENDANCE'
      pc.disable = 0 ;

其次，您应该尝试在表上建立索引。很难说最好的索引是什么，所以尝试添加以下内容：

• attr2(year, month, report, church_id, the_val)
• basic_data(id, province, parish)
• province_create(province, disable)

即使需要SELECT DISTINCT，该索引也应该有所帮助。但是，您需要了解为什么会出现重复并解决该问题的根本原因以获得最佳性能。