优化具有 DISTINCT 关键字和函数的 SQL 查询

Question

我有这个查询，它生成大约 40,000 条记录，这个查询的执行时间大约是 1 分 30 秒。

SELECT DISTINCT
a.ID,
a.NAME,
a.DIV,
a.UID,
(select NAME from EMPLOYEE where UID= a.UID and UID<>'') as boss_id, 
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 1 and id = a.ID) as TERM1,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 2 and id = a.ID) as TERM2,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 3 and id = a.ID) as TERM3,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 4 and id = a.ID) as TERM4,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 5 and id = a.ID) as TERM5,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 6 and id = a.ID) as TERM6,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 7 and id = a.ID) as TERM7,
(select DATE(MAX(create_time)) from XYZ where XYZ_ID= 8 and id = a.ID) as TERM8
FROM EMPLOYEE a
WHERE ID LIKE 'D%'

我尝试使用 group by、不同类型的连接来缩短执行时间，但未能成功。ABC 和 XYZ 表都已编入索引。 另外，我认为这个问题的根本原因是DISTINCT 关键字或MAX 函数。 如何优化上述查询以将执行时间缩短到至少不到一分钟？

感谢任何帮助。

Answer 1

查询未经测试，这只是关于如何以两种不同方式完成此操作的一个想法。

(SQL Server solutions here)

1. 对每个 ID 使用 LEFT JOIN 应该如下所示：

    SELECT a.ID,
           a.NAME,
           a.DIV,
           a.UID,
           b.Name as boss_id, 
           MAX(xyz1.create_time) as TERM1,
           MAX(xyz2.create_time) as TERM2,
           MAX(xyz3.create_time) as TERM3,
           MAX(xyz4.create_time) as TERM4,
           MAX(xyz5.create_time) as TERM5,
           MAX(xyz6.create_time) as TERM6,
           MAX(xyz7.create_time) as TERM7,
           MAX(xyz8.create_time) as TERM8
   FROM EMPLOYEE a
       JOIN EMPLOYEE b on a.UID = b.UID and b.UID <> ''
       LEFT JOIN XYZ xyz1 on a.ID = xyz1.ID and xyz1.XYZ_ID = 1
       LEFT JOIN XYZ xyz2 on a.ID = xyz2.ID and xyz1.XYZ_ID = 2
       LEFT JOIN XYZ xyz3 on a.ID = xyz3.ID and xyz1.XYZ_ID = 3
       LEFT JOIN XYZ xyz4 on a.ID = xyz4.ID and xyz1.XYZ_ID = 4
       LEFT JOIN XYZ xyz5 on a.ID = xyz5.ID and xyz1.XYZ_ID = 5
       LEFT JOIN XYZ xyz6 on a.ID = xyz6.ID and xyz1.XYZ_ID = 6
       LEFT JOIN XYZ xyz7 on a.ID = xyz7.ID and xyz1.XYZ_ID = 7
       LEFT JOIN XYZ xyz8 on a.ID = xyz8.ID and xyz1.XYZ_ID = 8
   WHERE a.ID LIKE 'D%'
   GROUP BY a.ID, a.NAME, a.DIV, a.UID, b.Name
   

2. 使用PIVOT 看起来像这样：

   select * from (
       SELECT DISTINCT
                   a.ID,
                   a.NAME,
                   a.DIV,
                   a.UID,
                   b.NAME as boss_id,
                   xyz.xyz_id,
                   xyz.create_time
       FROM EMPLOYEE a
           JOIN EMPLOYEE b on a.UID = b.UID and b.UID <> ''
           LEFT JOIN (SELECT DATE(MAX(create_time)) create_time, XYZ_ID, ID 
                      from XYZ 
                      where XYZ_ID between 1 and 8 
                      group by XYZ_ID, ID) xyz on a.ID = xyz1.ID
       WHERE a.ID LIKE 'D%') src
   PIVOT (
       max(create_time) for xyz_id IN (['1'], ['2'], ['3'], ['4'], 
                                       ['5'], ['6'], ['7'], ['8'])
   ) PIV
   

试一试

Answer 2

我会推荐group by 和条件聚合：

SELECT e.ID, e.NAME, e.DIV, e.UID,
       DATE(MAX(CASE WHEN XYZ_ID = 1 THEN create_time END)) as term1,
       DATE(MAX(CASE WHEN XYZ_ID = 2 THEN create_time END)) as term2,
       DATE(MAX(CASE WHEN XYZ_ID = 3 THEN create_time END)) as term3,
       DATE(MAX(CASE WHEN XYZ_ID = 4 THEN create_time END)) as term4,
       DATE(MAX(CASE WHEN XYZ_ID = 5 THEN create_time END)) as term5,
       DATE(MAX(CASE WHEN XYZ_ID = 6 THEN create_time END)) as term6,
       DATE(MAX(CASE WHEN XYZ_ID = 7 THEN create_time END)) as term7,
       DATE(MAX(CASE WHEN XYZ_ID = 8 THEN create_time END)) as term8
FROM EMPLOYEE e LEFT JOIN
     XYZ
     ON xyz.ID = e.id
WHERE e.ID LIKE 'D%'
GROUP BY e.ID, e.NAME, e.DIV, e.UID;

我不明白boss_id 的逻辑，所以我把它省略了。这应该会显着提高性能。