Question

我有一个有两个表的数据库。一个Call_Info表，其中包含有关传入/传出呼叫的详细信息，并具有名为Call_ID的唯一ID。我有一个第二个表链接并称为After_Call_Work表。

每次通话只有一次通话后工作记录。数据集有点混乱，对于同一个呼叫，有时会有3或4个呼叫工作记录。在进行查询时，如何只检索该特定呼叫的最早呼叫后工作记录而忽略其余的呼叫？我想象使用SQL函数First_Value但它似乎不是正确的。

使用Microsoft SQL Server 2012。

有什么想法吗？

Answer 1

这可以通过利用Window Function

来实现

WITH call_List
AS
(
    SELECT  Call_ID, OtherColumns, DateColumn,
            ROW_NUMBER() OVER (PARTITION BY Call_ID ORDER BY DateColumn ASC) rn
    FROM    After_Call_Work 
)
SELECT  a.*, b.OtherColumns, b.DateColumn
FROM    Call_Info a
        INNER JOIN call_List b
            ON a.Call_ID = b.Call_ID
WHERE   b.rn = 1

Answer 2

您应该可以使用select top，如下所示：

SELECT TOP 1
FROM call_info ci JOIN after_call_work acw ON ci.call_id=acw.call_id
ORDER BY acw.work_time DESC
WHERE ci.call_id=<your_call_id>

Answer 3

 WITH g AS (SELECT ROW_NUMBER() OVER (PARTITION BY callid 
ORDER BY date ASC) AS row,* from after_call_work
select * from call_info cinfo inner join g on 
cinfo.callid = g.callid and g.row=1

SQL检索第一个匹配行

3 个答案: