IF ELSE return wrong value in SQL Server

Question

I have a script that need to return the DATETIME from IF ELSE condition. But my return value from this got a wrong value here.

So this is my script

DECLARE @last_date SMALLDATETIME;
DECLARE @end_date SMALLDATETIME;
DECLARE @initial_date SMALLDATETIME;
DECLARE @begin_date SMALLDATETIME;
DECLARE @datediff int;
DECLARE @date_day int;

SET @last_date = NULL;
SET @datediff = NULL;
SET @initial_date = NULL;

IF (@datediff = '' or @datediff is NULL)
    SET @datediff = 5;
ELSE
    SET @datediff = @datediff;

IF (@last_date = '' or @last_date is NULL)
    SET @end_date = DATEADD(MONTH, DATEDIFF(MONTH, -1, GETDATE())-1, -1);
ELSE
    SET @end_date = DATEADD(MONTH, DATEDIFF(MONTH, -1, @last_date)-1, -1);

IF (@initial_date = '' or @initial_date is NULL)
    SET @begin_date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @end_date)-@datediff, 0);
ELSE
    SET @begin_date = @initial_date;
    SET @end_date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @begin_date)+@datediff, DATEPART(d,@initial_date));

print(@begin_date)
print(@end_date)

From this logic, it should take a value like this

• begin_date = Dec 1 2020 12:00AM
• end_date = May 31 2021 12:00AM

but it only return value

• begin_date = Dec 1 2020 12:00AM

But from that script why it entered to ELSE condition @initial_date ? is there any something wrong from my script?

Answer 1

If I understand your issue correctly, the reason for this unexpected result is that the last line ( SET @end_date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @begin_date) + @datediff, DATEPART(d, @initial_date)); ) is outside the IF.. ELSE block and always sets the value of @end_date to NULL . Probably an appropriate BEIGN.. END block in the last IF..ELSE statement will solve this issue:

...
IF (@initial_date = '' or @initial_date is NULL)
    SET @begin_date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @end_date)-@datediff, 0);
ELSE BEGIN
    SET @begin_date = @initial_date;
    SET @end_date = DATEADD(MONTH, DATEDIFF(MONTH, 0, @begin_date)+@datediff, DATEPART(d,@initial_date));
END