CASE expression for NULL condition is not working

Question

I have an SQL query where the case expression is not working because I am getting the NULL value.

Any idea how to fix this?

select 
td.reportEndDate,
    CASE td.originalLinearAirDate
    WHEN NULL THEN '12345678'
    END As originalLinearAirDate
from 
FROM DBA.Telecast td 
where id = 2
order by
td.reportEndDate,
originalLinearAirDate;

Answer 1

You can use COALESCE() :

SELECT td.reportEndDate, 
       COALESCE(td.originalLinearAirDate, '12345678') AS originalLinearAirDate -- Use default date instead of '12345678'
FROM DBA.Telecast td 
WHERE id = 2
ORDER BY td.reportEndDate, originalLinearAirDate;

In your case expression you didn't specified ELSE part hence you got NULL .

However, case expression will only return one type. So, you should check code or do necessary conversation.

Answer 2

You can use isnull

select 
td.reportEndDate,
    CASE WHEN td.originalLinearAirDate IS NULL THEN '19000101'
         ELSE td.originalLinearAirDate 
    END As originalLinearAirDate
from 
FROM DBA.Telecast td 
where id = 2
order by
td.reportEndDate,
originalLinearAirDate;

Answer 3

The problem is the NULL comparison. The comparison is never true, even when used from comparison in a CASE expression.

If you wanted to do this using CASE , then you need to use IS NULL :

(CASE WHEN td.originalLinearAirDate IS NULL
      THEN '12345678'
 END) As originalLinearAirDate

If you want to return the original value in this case, you need an ELSE :

(CASE WHEN td.originalLinearAirDate IS NULL
      THEN '12345678'
      ELSE td.originalLinearAirDate 
 END) As originalLinearAirDate

Note that this will return an error if the column is really a DATE , because '12345678' cannot be converted to a date.

This version is better expressed using COALESCE() :

COALESCE(td.originalLinearAirDate, '12345678')