Question

我的目的是将源表中的数据插入目标表。源表有datetime2列，目标表有datetime列。如果datetime2值不适合（<1753年）到datetime字段，则会转换为null。这是一个例子

DROP TABLE dbo.test1
--source table
CREATE TABLE dbo.test1 (wday DATETIME2 NULL)
go

INSERT  INTO dbo.test1
        (wday
        )
        SELECT  '2008-02-01 00:00:00.000'
        UNION ALL
        SELECT  '2009-02-01 00:00:00.000'
        UNION ALL
        SELECT  '0001-02-01 00:00:00.000'

DROP TABLE dbo.test2
--target table
CREATE TABLE dbo.test2 (wday DATETIME NULL)
go

--insert only valid datetime dates, < 1753 will be converted to nulls
INSERT INTO dbo.test2
        (wday
        )
        SELECT  CASE WHEN DATEDIFF(YEAR, dbo.test1.wday, GETDATE()) < 111
                     THEN NULL
                     ELSE CAST(dbo.test1.wday AS DATETIME)
                END
        FROM    dbo.test1

代码不起作用。另外在这里使用datediff是无效的逻辑，如何实现呢？

Answer 1

为什么不只是

INSERT  dbo.test2
        (wday
        )
        SELECT  CASE WHEN dbo.test1.wday < '17530101'
                     THEN NULL
                     ELSE CAST(dbo.test1.wday AS DATETIME)
                END
        FROM    dbo.test1

Answer 2

另一种选择：

--insert only valid datetime dates, < 1753 will be converted to nulls
INSERT INTO dbo.test2
        (wday
        )
        SELECT  CASE WHEN DATEPART(YEAR, dbo.test1.wday) < 1753
                     THEN NULL
                     ELSE CAST(dbo.test1.wday AS DATETIME)
                END
        FROM    dbo.test1

SQL Server：如果“datetime2”＆lt; 1753，然后“datetime”为NULL？

2 个答案: