CASE SQL返回Null

Question

When I execute the below in TSQL I get NULL even though there is a value.

Here's my code:

CASE
    WHEN cal.Weekday = ' ' OR HOLIDAY.DateInfo > ' '
        THEN WEPHWORK.WEPHWORK + OCESAWD.OCESAWD + OCESAWE.OCESAWE 
    ELSE OCESAWD.OCESAWD + OCESAWE.OCESAWE
END as weighted

Why is this happening?

Answer 1

Do you know your SQL truth tables?

( NULL = ' ' )  --> UNKNOWN
( NULL > ' ' )  --> UNKNOWN
( ( NULL = ' ' ) OR ( NULL > ' ' ) )  --->  ( UNKNOWN OR UNKNOWN )  --> UNKNOWN
( ( 'x' = ' '  ) OR ( NULL > ' ' ) )  --->  (   FALSE OR UNKNOWN )  --> UNKNOWN
( ( ' ' = ' '  ) OR ( NULL > ' ' ) )  --->  (    TRUE OR UNKNOWN )  --> TRUE

The last case can often catch people out.

Also do you know you SQL padding rules...?

Answer 2

Most likely, it is because at least one of your values is NULL .

In T-SQL, the basic rule is:

NULL + anything = NULL

To check why it is returning NULL , try the following piece of SQL. It will show you all your values laid out together so you can see why the NULL is being returned.

SELECT *
FROM (
    SELECT WEPHWORK.WEPHWORK,
        OCESAWD.OCESAWD,
        OCESAWE.OCESAWE,
        CASE
            WHEN cal.Weekday = ' ' OR HOLIDAY.DateInfo > ' '
                1
            ELSE 2
        END as type
        CASE
            WHEN cal.Weekday = ' ' OR HOLIDAY.DateInfo > ' '
                THEN WEPHWORK.WEPHWORK + OCESAWD.OCESAWD + OCESAWE.OCESAWE
            ELSE OCESAWD.OCESAWD + OCESAWE.OCESAWE
        END as weighted
    FROM your_tables.... ) x
WHERE x.weighted IS NULL