How to check a column values is null or not in select statement

Question

I am new to SQL Server, and I want to validate whether a column value is NULL or empty in the select statement .

The select statement is :

SELECT COM_TYPE, COM_IN_CHARGE_POSITION 
FROM TABLE_01 

If the COM_TYPE value is null or empty, I want to take the COM_TYPE_OTHERS value as COM_TYPE for the same way to COM_IN_CHARGE_POSITION .

It's simply if the COM_TYPE and COM_IN_CHARGE_POSITION is null or empty I want to take the values from other two columns.

Can anyone help me to solve this?

Answer 1

Let me assume that blank is NULL . In that case, you simply want coalesce() :

select coalesce(COM_TYPE, COM_TYPE_OTHERS, COM_IN_CHARGE_POSITION, COM_IN_CHARGE_POSITION_OTHERS) as effective_COM_TYPE

The coalesce() function takes the first non- NULL argument. If the values could be empty strings or strings with spaces in addition to NULL , then a case expression is recommended.

Answer 2

COALESCE function can check which one column is first non-NULL, but you, if you want to check, is null or empty you can try to use CASE WHEN

SELECT  CASE WHEN COM_TYPE IS NULL OR COM_TYPE = '' THEN COM_TYPE_OTHERS 
             ELSE COM_TYPE END AS COM_TYPE,
        CASE WHEN COM_IN_CHARGE_POSITION IS NULL OR COM_IN_CHARGE_POSITION = '' THEN COM_IN_CHARGE_POSITION_OTHERS 
             ELSE COM_IN_CHARGE_POSITION END AS COM_IN_CHARGE_POSITION,
FROM TABLE_01 

Answer 3

You can use COALESCE() or ISNULL() OR CASE WHEN statement

SELECT COALESCE( COM_TYPE, COM_TYPE_OTHERS ) AS COM_TYPE,
       COALESCE (COM_IN_CHARGE_POSITION , COM_IN_CHARGE_POSITION_OTHERS) AS COM_IN_CHARGE_POSITION 
FROM   TABLE_01

Answer 4

Simplest way to check for null or empty is to use ISNULL and NULLIF :

SELECT ISNULL(NULLIF(COM_TYPE, ''), COM_TYPE_OTHERS)
FROM TABLE_01

You can also use COALESCE but it does not check for empty string (only null), so you will still have to use NULLIF .

Also note that ISNULL is faster than COALESCE even if the difference is pretty negligible.