IF Inside WHERE with stored procedure - sql

Question

I have a WHERE statement that looks like this:
WHERE
((#Value1 IS NULL AND [value1_id] IS NULL) OR [value1_id] = ISNULL(#Value1, [value1_id]))
AND
((#Value2 IS NULL AND [value2_id] IS NULL) OR [value2_id] = ISNULL(#Value2, [value2_id]))
AND
((#Value3 IS NULL AND [value3_id] IS NULL) OR [value3_id] = ISNULL(#Value3, [value3_id]))
AND
((#Value4 IS NULL AND [value4_id] IS NULL) OR [value4_id] = ISNULL(#Value4, [value4_id]))
AND
((#Value5 IS NULL AND [value5_id] IS NULL) OR [value5_id] = ISNULL(#Value5, [value5_id]))
AND
((#Value6 IS NULL AND [value6_id] IS NULL) OR [value6_id] = ISNULL(#Value5, [value6_id]))
I need to add some conditional logic inside of the WHERE so I can do special things with Value5 and Value6. Basically, if Value5, Value6, or another value is null, I want to use the Value 5 and Value 6 lines as is. If all three values aren't NULL, I need to run some calculations on the values.
Any ideas on what the best action would be?

Answer 1

Use CASE
"CASE can be used in any statement or clause that allows a valid expression. For example, you can use CASE in statements such as SELECT, UPDATE, DELETE and SET, and in clauses such as select_list, IN, WHERE, ORDER BY, and HAVING."
http://msdn.microsoft.com/en-us/library/ms181765.aspx
You can perform calculations inside of a SELECT like this:
SELECT
CASE
WHEN #Value7 is not null THEN #Value7 * 100
ELSE Value7 * 100
END
FROM #T
WHERE (#Value1 is null and Value1 is null)
AND (#Value2 is null and Value2 is null)
It's still not very clear what exactly you're trying to accomplish. Is the WHERE not inside a SELECT? Provide a clear, concise example if the above is not correct.

Answer 2

Basically, if Value5, Value6, or another value is null, I want to use
the Value 5 and Value 6 lines as is. If all three values aren't NULL,
I need to run some calculations on the values.
I think this will be hard to do with for example a CASE inside the WHERE clause. You might be better off with an IF construction outside of your SELECT statements:
IF (#Value5 IS NULL OR #Value6 IS NULL OR #OtherValue IS NULL)
BEGIN
<Statement1AsIs>
END
ELSE
BEGIN
<Statement2WithComputations>
END
Rewrite WHERE clause
On a short sidenote, I know you did not ask for it, but I have the feeling there must be a 'clearer' way to write these
((#Value1 IS NULL AND [value1_id] IS NULL) OR [value1_id] = ISNULL(#Value1, [value1_id]))
I've been playing around a bit and this is one way to say the same:
COALESCE(#Value1, [value1_id], 1001) = COALESCE([value1_id], 1001)
This is another one, equivalent and shorter:
#Value1 IS NULL OR [value1_id] = ISNULL(#Value1, [value1_id])
Check out this SQL Fiddle to see the equivalence.