Sql 为表中的每个ID选择最新的3条记录

我有一个带有复合主键（

ID

，

Date

）的表，如下所示

+------+------------+-------+ | ID | Date | Value | +------+------------+-------+ | 1 | 1433419200 | 15 | | 1 | 1433332800 | 23 | | 1 | 1433246400 | 41 | | 1 | 1433160000 | 55 | | 1 | 1432900800 | 24 | | 2 | 1433419200 | 52 | | 2 | 1433332800 | 23 | | 2 | 1433246400 | 39 | | 2 | 1433160000 | 22 | | 3 | 1433419200 | 11 | | 3 | 1433246400 | 58 | | ... | ... | ... | +------+------------+-------+

---

这里的快速解决方案是什么？

首先，这里是对不等式方法的正确查询：

SELECT p1.ID, p1.Date, p1.Value
FROM MyTable p1 LEFT JOIN
     MyTable AS p2 
     ON p1.ID = p2.ID AND p2.Date <= p1.Date
--------------------------^ fixed this condition
GROUP BY p1.ID, p1.Date, p1.Value
HAVING COUNT(*) <= 5
ORDER BY p1.ID, p1.Date DESC;

选择p1.ID、p1.Date、p1.Value
从MyTable p1左联接
MyTable作为p2
在p1.ID=p2.ID和p2.Date上，您可以查找每个ID的三个最近日期：

SELECT ID, Date, Value
FROM MyTable
WHERE Date IN (SELECT Date
               FROM MyTable AS T2
               WHERE T2.ID = MyTable.ID
               ORDER BY Date DESC
               LIMIT 3)

或者，查找每个ID的第三个最近日期，并将其用作限制：

SELECT ID, Date, Value
FROM MyTable
WHERE Date >= IFNULL((SELECT Date
                      FROM MyTable AS T2
                      WHERE T2.ID = MyTable.ID
                      ORDER BY Date DESC
                      LIMIT 1 OFFSET 2),
                     0)

这两个查询都应该从主键的索引中获得良好的性能。
实际上，“可选”修复是必要的。我刚刚尝试过，如果没有额外的两个
groupby
列，它仍然不会返回任何结果。在索引点上，由于
ID
和
Date
构成复合主键，因此默认情况下它们上有一个索引。但是查询在大约600K行的表上运行几乎需要18秒。这是一种不同的方法，也是一种非常好的方法。性能提高了10倍！
SELECT distinct x.ID,x.Date,X.Value
FROM ( SELECT DISTINCT ID FROM XXXTable  ) c
    CROSS APPLY (

    select top 3 A.ID,a.Date,Value,[Count] from (
    SELECT distinct ID,Date,Value, ROW_NUMBER()
    over (
        PARTITION BY ID
        order by Date
    ) AS [Count]  where c.ID = t.ID


    ) A  order by [Count] desc

SELECT distinct x.ID,x.Date,X.Value
FROM ( SELECT DISTINCT ID FROM XXXTable  ) c
    CROSS APPLY (

    select top 3 A.ID,a.Date,Value,[Count] from (
    SELECT distinct ID,Date,Value, ROW_NUMBER()
    over (
        PARTITION BY ID
        order by Date
    ) AS [Count]  where c.ID = t.ID


    ) A  order by [Count] desc