SQL select all if parameter is null else return specific item

Question

Is there a way to write the following script so that it returns all products if the ProductID variable is null ? And return a specific product when the product it is not nul

Answer 1

Try this

DECLARE @productID INT = NULL

SELECT 
    ProductID,
    ProductName,
    ProductDesc 
FROM
    product 
WHERE 
    ProductID = isnull(@productID,ProductID)

Answer 2

Performance is a incredible better when using CASE statement:

SELECT ProductID, ProductName,ProductDesc 
FROM product 
WHERE ProductID = CASE WHEN @productID IS NULL THEN ProductID ELSE @productID END

ISNULL() prevents the optimizer using an index on that column.

Answer 3

Use case statement:

SELECT ProductID, ProductName,ProductDesc 
FROM product 
WHERE ProductID = CASE WHEN @productID IS NULL THEN ProductID ELSE @productID END

Or IIF() function if you’re using SQL Server 2012:

SELECT ProductID, ProductName,ProductDesc 
FROM product 
WHERE ProductID =IIF(@productID IS NULL, ProductID, @productID )

Answer 4

SELECT
    ProductID,
    ProductName,
    ProductDesc 
FROM
    product 
WHERE
    ProductID = CASE WHEN @productID IS NULL THEN ProductID ELSE @productID END

Answer 5

Since "" is not recognized as NULL I used value

SELECT ProductID, ProductName,ProductDesc 
FROM product 
WHERE ProductID =IIF(@productID =1, ProductID, @productID )

In my code:

 MyDataAdapter.SelectCommand.Parameters("@productID").Value = 1

Answer 6

Why not just:

DECLARE @productID INT = NULL

SELECT ProductID, ProductName,ProductDesc 
FROM   product 
WHERE  ProductID = @productID
OR     @productID IS NULL;

Here a demo in SQLFiddle with NULL and a value for @productID