Question

这应该是一个简单的UPDATE，我认为应该在两个不同的列上两次更新相同的记录，但它不起作用。

简化的示例代码：

DECLARE @nowWithDate DATETIME = GETDATE()
DECLARE @result TABLE(Id INT, Poll1Date DATETIME, Poll2Date DATETIME)

INSERT INTO @result VALUES(1, NULL, NULL)

;WITH data(Id, IsPoll1, IsPoll2) AS
(
    SELECT 1, 1, 0
    UNION ALL
    SELECT 1, 0, 1
)
UPDATE r
SET Poll1Date = IIF(d.IsPoll1 = 1, @nowWithDate, Poll1Date),
    Poll2Date = IIF(d.IsPoll2 = 1, @nowWithDate, Poll2Date)
FROM @result r
JOIN data d ON d.Id = r.Id

SELECT * FROM @result

我无法弄清楚，为什么第二个日期没有更新？看起来这行只更新一次。

Answer 1

DECLARE @nowWithDate DATETIME = GETDATE()
DECLARE @result TABLE(Id INT, Poll1Date DATETIME, Poll2Date DATETIME)

INSERT INTO @result VALUES(1, NULL, NULL)

;WITH data(Id, IsPoll1, IsPoll2) AS
(
    SELECT 1, 1, 0
    UNION ALL
    SELECT 1, 0, 1
)
select * from data

返回2行。因此，当您使用@results加入时，它仅从第一行更新。对于第一行，IsPoll1 = 1但IsPoll2 = 0，因此，第二行未更新。

更新两行

DECLARE @nowWithDate DATETIME = GETDATE()
DECLARE @result TABLE(Id INT, Poll1Date DATETIME, Poll2Date DATETIME)

INSERT INTO @result VALUES(1, NULL, NULL)

;WITH data(Id, IsPoll1, IsPoll2) AS
(
select Id, SUM (IsPoll1),SUM(IsPoll2) from(
    SELECT 1 as Id, 1 as IsPoll1, 0 as IsPoll2
    UNION ALL
    SELECT 1 as Id,0 as IsPoll1,  1 as IsPoll2) d1
    group by d1.Id
)
UPDATE r
SET Poll1Date = IIF(d.IsPoll1 = 1, @nowWithDate, Poll1Date),
    Poll2Date = IIF(d.IsPoll2 = 1, @nowWithDate, Poll2Date)
FROM @result r
JOIN data d ON d.Id = r.Id

SELECT * FROM @result

根据JOIN更新两列

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