SQL：DATEDIFF如果开始日期大于另一个字段中的日期

Question

I'm looking to work out the difference between 2 dates that I have declared as variables,

DECLARE @start_date DATETIME
SET @start_date= '20000728'

DECLARE @end_date DATETIME
SET @end_date= '20161028'

But only if @start_date is greater than DATE_CREATED. If it is not I want to do the difference between DATE_CREATED and @end_date

How can I go about doing this?

All I have at the moment is:

DATEDIFF(DAY, @start_date, @end_date) AS 'DAYS_AVAIL_RANGE'

I'm not sure how I go about incorporating an IF statement to do this,

Any help is appreciated, cheers!

Answer 1

Try this. This will definitely solve your problem as here casting is performed for date/time value.

select
    case when DATEDIFF(day,convert(date,DATE_CREATED),CONVERT(date,@start_date)) > 0
        then datediff(DAY, convert(date,@start_date), convert(date,@end_date))
    else
        datediff(DAY, convert(date,DATE_CREATED), convert(date,@end_date)) 
    end

Answer 2

You want case :

select (case when @start_date > date_created
             then datediff(DAY, @start_date, @end_date) 
             else datediff(DAY, date_created, @end_date) 
        end) as days_avail_range

Answer 3

尝试这个

 select datediff(DAY, (select max(v) from (VALUES (@start_date), (DATE_CREATED)) as value(v)) , @end_date) from yourtable