T-SQL Query null issue - sql

Question

I want to write a stored procedure which will return true or false based on the following condition:
if 2 columns in all the rows in a result set are null, then return true
if at least one is not null, then return false
Like for example in the following query
select *
from Products
where productID = 123
and ProductType is null
and ProductDate is null
The above query can return 1 row or return 100 rows, so if all are null, then it will return true; if at least 1 is not null, then it will return false.

Answer 1

Given this sample data and desired results:
CREATE TABLE dbo.Products
(
ProductID int,
ProductType int,
ProductDate date
);
INSERT dbo.Products(ProductID, ProductType, ProductDate)
VALUES
(123, NULL, NULL),(123, NULL, NULL), -- this should return 1
(456, 5, NULL), (456, NULL, NULL), -- this should return 0
(789, NULL, GETDATE()); -- this should return 0
We can do:
CREATE PROCEDURE dbo.whatever1
#ProductID int
AS
BEGIN
DECLARE #return int = CASE WHEN EXISTS (SELECT 1
FROM dbo.Products
WHERE productID = #ProductID
AND (ProductType IS NOT NULL OR ProductDate IS NOT NULL)
) THEN 0 ELSE 1 END;
RETURN #return;
END
Then to execute:
DECLARE #hr int;
EXEC #hr = dbo.whatever1 #ProductID = 123;
SELECT #hr;
EXEC #hr = dbo.whatever1 #ProductID = 456;
SELECT #hr;
EXEC #hr = dbo.whatever1 #ProductID = 789;
SELECT #hr;
Results:
1
0
0
The tricky bit is when you say "return" we're not quite sure if you mean the explicit RETURN keyword, or an OUTPUT parameter, or a resultset. I feel like an OUTPUT parameter would be more appropriate in this case, since RETURN is generally reserved for error/status (and can only be an int). So we can use a more appropriate type depending on what we need:
CREATE PROCEDURE dbo.whatever2
#ProductID int,
#return bit OUTPUT
AS
BEGIN
SET #return = CASE WHEN EXISTS (SELECT 1
FROM dbo.Products
WHERE productID = #ProductID
AND (ProductType IS NOT NULL OR ProductDate IS NOT NULL)
) THEN 0 ELSE 1 END;
END
Then to execute:
DECLARE #return bit;
EXEC dbo.whatever2 #ProductID = 123, #return = #return OUTPUT;
SELECT #return;
EXEC dbo.whatever2 #ProductID = 456, #return = #return OUTPUT;
SELECT #return;
EXEC dbo.whatever2 #ProductID = 789, #return = #return OUTPUT;
SELECT #return;
Results:
1
0
0
Working example here (though be aware that fiddle displays bit as true/false instead of 1/0): db<>fiddle
If either of these procedures don't work like you expect, please adjust the fiddle with your sample data that you think is producing wrong results, and please be specific about what you mean by "return" and "always give me a value of" - we have no idea where you are seeing 1 and why you would expect to see 0.

Answer 2

Try:
IF EXISTS (SELECT 1 FROM Products WHERE ProductID = 123 AND (ProductType IS NOT NULL OR ProductDate IS NOT NULL))
SELECT CAST (0 AS bit)
ELSE
SELECT CAST (1 AS bit)
Using exists is more efficient than a count since it will only scan the table until the condition is met. Count will always scan the whole table.

Answer 3

select IIF(COUNT(*) = 0, 'true','false')
from Products
where productID=#ProductID and ProductType is null and ProductDate is null