Question

我想做的是：

SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN (SELECT TOP 1 *
            FROM SubQueryTable sq
            WHERE sq.ForeignID = j.ID
            ORDER BY VersionColumn DESC)

所以基本上，从SubQueryTable，我只想检索一行，对于具有我可以从JoinedTable获得的特定ID的所有行，VersionColumn具有最大值。

T-SQL不允许我这样做，解决这个问题的好方法是什么？

我想要阻止的是加载整个SubQueryTable并在过晚时进行过滤....

SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN (SELECT TOP 1 *
            FROM SubQueryTable sq
            ORDER BY VersionColumn DESC) sj ON sj.ForeignID = j.ID

我担心第二个版本首先执行非常慢的子查询，只在加载了所有行时才对其进行过滤，但我希望尽快过滤。

有什么想法吗？

Answer 1

如果您在VersionColumn

上有索引，这将表现良好

SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
CROSS APPLY (SELECT TOP 1 *
            FROM SubQueryTable sq
            WHERE  sq.ForeignID = j.ID
            ORDER BY VersionColumn DESC) sj

Answer 2

回答：

您好，

以下查询我根据您的要求使用国家/地区，州和城市表创建。

SELECT * FROM (
SELECT  m.countryName, j.StateName,c.CityName , ROW_NUMBER() OVER(PARTITION BY c.stateid ORDER BY c.cityid desc) AS 'x'
FROM CountryMaster m
INNER JOIN StateMaster j on j.CountryID = m.CountryID
INNER JOIN dbo.CityMaster c ON j.StateID = c.StateID 
) AS numbered WHERE x = 1

以下是您的解决方案，以上仅供您参考。

SELECT * FROM (
SELECT  m.MainTablecolumnNm, j.JoinedTablecolumnNm,c.SubQueryTableColumnName , ROW_NUMBER()
OVER(PARTITION BY sj.ForeignID ORDER BY c.sjID desc) AS 'abc'
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN SubQueryTable sj ON sj.ForeignID = j.ID 
) AS numbered WHERE abc = 1

谢谢， Vishal Patel

如何在与子查询的连接中使用连接表中的列

2 个答案: