我有两个表都包含员工数据,TableA
和 TableB
,我根据 2 个 ID(其中一个是 userID
)加入它们另一个 mID
(基于月份的 id))使用 LEFT OUTER JOIN
,它在大约 20% 的结果中返回 NULL,因为 TableB
它不完整。我想要 - 如果可能 - 一个查询来检测连接是否找不到匹配项,并减去一个月的 mID
以便 JOIN 可以仅用旧数据覆盖至少一部分丢失的数据。
我不知道这是否是一个太复杂的查询,但我想到的是:
SELECT T1.*, T2.*
FROM TABLEA
LEFT OUTER JOIN TABLEB
ON T2.USERID = T1.USERID AND (CASE WHEN (T2.HID = T1.HID) = NULL THEN (T2.HID = T1.HID-1))
感谢任何帮助。
最佳答案
我认为这才是你真正想做的;缺点是有更多的逻辑,并且每列都会重复,但它提供了精细的控制。
DECLARE @TableA TABLE (USERID INT,HID INT,SomeData VARCHAR(20))
DECLARE @TableB TABLE (USERID INT,HID INT,SomeData VARCHAR(20))
INSERT INTO @TableA(USERID,HID,SomeData) SELECT 1,5,'Now'
INSERT INTO @TableA(USERID,HID,SomeData) SELECT 2,5,NULL
INSERT INTO @TableA(USERID,HID,SomeData) SELECT 3,5,NULL
INSERT INTO @Tableb(USERID,HID,SomeData) SELECT 2,4,'Now-1'
INSERT INTO @Tableb(USERID,HID,SomeData) SELECT 2,3,'Now-2'
INSERT INTO @Tableb(USERID,HID,SomeData) SELECT 3,4,'Now-1'
SELECT
t1.USERID, T1.Hid AS [Current HID]
,
CASE
WHEN T1.SomeData IS NOT NULL THEN T1.SomeData
WHEN T2.USERID IS NOT NULL THEN T2.SomeData
WHEN T3.USERID IS NOT NULL THEN T3.SomeData
ELSE T1.SomeData
END AS [Most Recent SomeData]
FROM @TABLEA T1
LEFT JOIN @TABLEB T2 ON T2.USERID = T1.USERID AND T2.HID = T1.HID
LEFT JOIN @TABLEB T3 ON T3.USERID = T1.USERID AND T3.HID = T1.HID-1
关于sql - SQL Server 中连接表时的条件,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55248165/