/* declare @datetime datetime set @datetime = '2018-08-27' select dbo.fn_trunc(@datetime, 'yyyy') as [本年第一天], dbo.fn_trunc(@datetime, 'qq') as [本季第一天quarter], dbo.fn_trunc(@datetime, 'mm') as [本月第一天month], dbo.fn_trunc(@datetime, 'dd') as [當天now], dbo.fn_trunc(@datetime, 'day') as [本周第一天weekday] -------------------------------------------------------------------------------- 本年第一天 本季第一天quarter 本月第一天month 當天now 本周第一天weekday ----------------------- ----------------------- ----------------------- ----------------------- ----------------------- 2018-01-01 00:00:00.000 2018-07-01 00:00:00.000 2018-08-01 00:00:00.000 2018-08-27 00:00:00.000 2018-08-26 00:00:00.000 -------------------------------------------------------------------------------- */ alter function dbo.fn_trunc( @datetime datetime, @datepart varchar(30) ) returns datetime as begin /* @datepart： yyyy: 本年度第一天 qq: 本季度第一天 q: 本季度第一天 mm: 本月第一天 dd: 當天 day: 本周第一天 */ declare @result datetime, @yyyy varchar(4), @qq int, @mm int, @dd varchar(4), @day varchar(4), @yyyymm varchar(10), @yyyymmdd varchar(10); if @datetime = '1900-01-01' set @datetime = null; if @datetime is null set @result = null; if (@datetime is not null) and (@datepart= 'yyyy') set @result = cast(datepart(yyyy, @datetime) as varchar(10)) + '-01-01' if (@datetime is not null) and (@datepart='qq') begin set @qq = datepart(qq,@datetime) if @qq = 1 set @result = cast(datepart(yyyy, @datetime) as varchar(10)) + '-01-01' ; if @qq =2 set @result = cast(datepart(yyyy, @datetime) as varchar(10)) + '-04-01' ; if @qq =3 set @result = cast(datepart(yyyy, @datetime) as varchar(10)) + '-07-01' ; if @qq =4 set @result = cast(datepart(yyyy, @datetime) as varchar(10)) + '-10-01' ; end; if (@datetime is not null) and (@datepart= 'mm') begin set @yyyymm = convert(varchar(7), @datetime, 120 ) -- 'yyyy-mm' set @result = @yyyymm + '-01' end; if (@datetime is not null) and (@datepart= 'dd') begin set @yyyymmdd = convert(varchar(10), @datetime, 120 ) -- 'yyyy-mm-dd' set @result = @yyyymmdd end; if (@datetime is not null) and (@datepart= 'day') begin set @result = DATEADD(Day,0-(DATEPART(Weekday,@datetime)+@@DATEFIRST-1)%7,@datetime) end; if @result is not null set @result = cast( @result as datetime); else set @result = null; return(@result) end go