Question

I have a SQL query which includes the following statement

SELECT
    (CASE 
        WHEN field1 > 0 THEN field1 
        ELSE (field2 * field3) 
    END) AS result
FROM table

Which is supposed to return the value of field1, unless that is ‘0’, in which case the statement returns the product of two other fields.

The issue I am having is this statement returns NULL if field1 is NULL.

I want to revise my SQL so that the product of fields 2 & 3 is returned when field1 is NULL, just as it does when field1 is ‘0’.

I have tried the following:

SELECT
    (CASE 
        WHEN field1 > 0 THEN field1 
        WHEN field1 IS NULL THEN (field2 * field3)
        ELSE (field2 * field3) 
    END) AS result
FROM table

But NULL still seems to permeate through the statement and NULL is still being returned whenever field1 is NULL.

Answer 1

Your query does already what you want. When field1 is NULL, it returns the product field2 * field3. If either of field2 or field3 though is NULL, the (returned) product will be NULL.

If you want to be returning some value (0 perhaps) when either of them is NULL, you can change the CASE:

SELECT
    (CASE 
        WHEN field1 > 0                         -- when field1 > 0
            THEN field1 
        WHEN field2 IS NULL OR field3 IS NULL   -- when field1 = 0 or NULL
            THEN 0
        ELSE field2 * field3 
    END) AS result
FROM table ;

or simply:

SELECT
    (CASE 
        WHEN field1 > 0  
            THEN field1 
        ELSE COALESCE(field2 * field3, 0) 
    END) AS result
FROM table ;