NULLs and SET ANSI_NULLS OFF - sql

Question

I have a bit of SQL that queries a table that has one column that can take NULL.
In the code below the #term_type_id could be NULL, and the column term_type_id could have NULL values.
So the code below works if #term_type_id has a value, but does not work if #term_type_id is NULL.
Setting SET ANSI_NULLS OFF is a way around the problem, but I do know that this will be depreciated at some stage.
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND term_type_id=#term_type_id
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
What I have done in the past is to have something like this
if #term_type_id is NULL
BEGIN
SELECT ......
WHERE .....
AND term_type_id IS NULL
END
BEGIN
SELECT ......
WHERE .....
AND term_type_id = #term_type_id
END
While this works, it is very verbose and makes the code hard to read and maintain.
Does anyone have a better solution than using SET ANSI_NULLS OFF or having to write conditional code just to manage the case when something could be a value or NULL?
BTW - When I use SET ANSI_NULLS OFF, I only do it for the specific query then turn it back on afterwards. I do understand the reasons why this is frowned upon, but it is at the expense of writing pointless code to get around a 'pure' view of NULL.
Ben

Answer 1

Since both the column and the parameter can be null, you should treat both cases:
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND ((term_type_id IS NULL AND #term_type_id IS NULL) OR term_type_id = #term_type_id)
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
Note that this will only return results when both column and parameter are null, or none of them is null.

Answer 2

Ben, a better solution to if #term_type_id is NULL SELECT #term_type_id=-1
would be to use isnull(#term_type_id,-1)

Answer 3

Ahh - yes - thank you for the prompt responses. I think I have just come up with a better solution (well in this case)...
if #term_type_id is NULL SELECT #term_type_id=-1
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND ISNULL(term_type_id,-1)=#term_type_id
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
This works in this case as term_type_id is the result of an identity (1,1) and thus can not be -1.

Answer 4

Try this, this will work on both case.
SELECT ......
WHERE .....
AND ISNULL(term_type_id,-1) = ISNULL(#term_type_id,-1)
You can use any static value instead of -1
Or you can use something like below
SELECT ......
WHERE .....
AND ( (#term_type_id IS NULL AND term_type_id IS NULL)
OR term_type_id = #term_type_id
)

Answer 5

If it's the only nullable column among your search criteria, the best way would be to split conditions within a single UNION statement:
select date, value from dbo.History
where term_type_id is null
-- Remaining search criteria
and ...
union all
select date, value from dbo.History
where term_type_id = #term_type_id
-- Remaining search criteria
and ...
This is the fastest code possible in your case, basically because SQL Server doesn't have a particular knack for OR-ed conditions. However, another nullable column will turn this into a rather unpleasant mess.
If you think you can sacrifice performance, there is a useful function in T-SQL that does exactly that - NULLIF():
select date, value from dbo.History
where nullif(#term_type_id, term_type_id) is null
-- Remaining search criteria
and ...
However, this type of condition will be non-SARGable, most likely. Also, note that the order of arguments does matter in NULLIF(). Alternatively, you can devise CASE constructs of various complexity that might be semantically more suitable to your exact requirements.