SQL date selection as NULL, After, Before, Between - sql

Question

Requirement: select by date as After, Before, Between or all if null
I'm using SQL Server 2008
This is my attempt but I'm getting syntax errors on code that is valid used outside of the case.
Is there a better method?
using case what is the correct syntax?
declare #StartDate datetime;
declare #EndDate datetime;
SET #EndDate = GETDATE();
SET #StartDate = DATEADD(year, -2, GETDATE());
select *
from ArCustomer
where CAST(Customer as int) > 1000
AND
CASE WHEN #StartDate IS NOT NULL AND #EndDate IS NOT NULL THEN
ArCustomer.DateLastSale BETWEEN #StartDate AND #EndDate
WHEN #StartDate IS NULL AND #EndDate IS NOT NULL THEN
ArCustomer.DateLastSale < #EndDate
WHEN #StartDate IS NOT NULL AND #EndDate IS NULL THEN
ArCustomer.DateLastSale > #StartDate
END;

Answer 1

Alternately, you could not restrict by the date parameter if it is NULL:
SELECT *
FROM ArCustomer ac
WHERE
CAST(ac.Customer as int) > 1000
AND (ac.DateLastSale >= #StartDate OR #StartDate IS NULL)
AND (ac.DateLastSale <= #EndDate OR #EndDate IS NULL)
Or... you can handle the NULL by treating it as the low-end or high-end date:
SELECT *
FROM ArCustomer ac
WHERE
CAST(ac.Customer as int) > 1000
AND ac.DateLastSale BETWEEN ISNULL(#StartDate, '1900-01-01')
AND ISNULL(#EndDate, '9999-12-31')
EDIT:
There could be a difference in the execution plan between these two approaches, so you might try both methods and see if one out-performs the other...

Answer 2

WHERE CAST(Customer as int) > 1000 AND
(#StartDate IS NULL OR #StartDate <= ArCustomer.DateLastSale) AND
(#EndDate IS NULL OR ArCustomer.DateLastSale <= #EndDate)

Answer 3

Please note that the below query should have * avoided and the specific column names should be mentioned.
declare #StartDate datetime;
declare #EndDate datetime;
SET #EndDate = GETDATE();
SET #StartDate = DATEADD(year, -2, GETDATE());
Declare #SQL Varchar(1000)
Set #SQL = 'select ColumnName
from ArCustomer
where CAST(Customer as int) > 1000
AND'
if(#StartDate IS NOT NULL AND #EndDate IS NOT NULL)
Begin
Set #SQL = #SQL + ' ArCustomer.DateLastSale BETWEEN ''' + Convert(varchar, #StartDate) +
''' AND ''' + Convert(varchar, #EndDate) + ''''
End
else if(#StartDate IS NULL AND #EndDate IS NOT NULL)
Begin
Set #SQL = #SQL + ' ArCustomer.DateLastSale < ''' + Convert(varchar, #EndDate) + ''''
End
else
Set #SQL = #SQL + ' ArCustomer.DateLastSale > ''' + Convert(varchar, #StartDate) + ''''
exec(#SQL)
Considered all cases.