使用DateDiff时的SQL动态DatePart

Question

有没有办法将DateDiff的DatePart参数作为变量传递？这样我可以编写与此类似的代码？

DECLARE @datePart VARCHAR(2)
DECLARE @dateParameter INT

SELECT @datePart = 'dd'
SELECT @dateParameter = 28

SELECT
    *
FROM
    MyTable
WHERE
    DATEDIFF(@datePart, MyTable.MyDate, GETDATE()) < @dateParameter

我能想到的唯一方法是使用CASE语句检查参数的值,或者将SQL构建为字符串并在EXEC中运行它.

有没有人有任何"更好"的建议？该平台是MS SQL Server 2005

Answer 1

根据SQL Server 2005的DATEDIFF(参数部分)上的BOL条目,

这些日期部分和缩写不能作为用户声明的变量提供.

因此,您可能会遇到动态SQL或使用CASE语句.但我会选择CASE版本而不是动态SQL.

Answer 2

虽然旧但但仍然有效.

我是这样做的,只是想分享代码,所以你不必做我必须做的所有烦人的打字.涵盖所有可能的日期部分.只需替换函数的名称和日期函数,以实现其他T-SQL日期函数.

复制和粘贴部分

-- SELECT dbo.fn_DateAddFromStringPart('year', 1, GETDATE())
CREATE FUNCTION fn_DateAddFromStringPart
(
    @Interval VARCHAR(11),
    @Increment INT,
    @Date SMALLDATETIME
)
RETURNS DATETIME
AS
BEGIN
    -- Declare the return variable here
    DECLARE @NewDate DATETIME

    -- Add the T-SQL statements to compute the return value here
    SELECT @NewDate = CASE
        WHEN @Interval IN ('year', 'yy', 'yyyy') THEN DATEADD(YEAR, @Increment, @Date)
        WHEN @Interval IN ('quarter', 'qq', 'q') THEN DATEADD(QUARTER, @Increment, @Date)
        WHEN @Interval IN ('month', 'mm', 'm') THEN DATEADD(MONTH, @Increment, @Date)
        WHEN @Interval IN ('dayofyear', 'dy', '') THEN DATEADD(DAYOFYEAR, @Increment, @Date)
        WHEN @Interval IN ('day', 'dd', 'd') THEN DATEADD(DAY, @Increment, @Date)
        WHEN @Interval IN ('week', 'wk', 'ww') THEN DATEADD(WEEK, @Increment, @Date)
        WHEN @Interval IN ('weekday', 'dw', 'w') THEN DATEADD(WEEKDAY, @Increment, @Date)
        WHEN @Interval IN ('hour', 'hh') THEN DATEADD(HOUR, @Increment, @Date)
        WHEN @Interval IN ('minute', 'mi', 'n') THEN DATEADD(MINUTE, @Increment, @Date)
        WHEN @Interval IN ('second', 'ss', 's') THEN DATEADD(SECOND, @Increment, @Date)
        WHEN @Interval IN ('millisecond', 'ms') THEN DATEADD(MILLISECOND, @Increment, @Date)
        WHEN @Interval IN ('microsecond', 'mcs') THEN DATEADD(MICROSECOND, @Increment, @Date)
        WHEN @Interval IN ('nanosecond', 'ns') THEN DATEADD(NANOSECOND, @Increment, @Date)
    END

    -- Return the result of the function
    RETURN @NewDate

END
GO