Question

Oracle 11g: Consider the following two CASE Statements

SEARCHED CASE

with null_table as (select null as null_set from dual )
select 
     case 
     when (null_set is null) then 'NULL INDEED'
     else 'NOTNULL?'
     end as AM_I_NULL_OR_NOT   
from null_table

SIMPLE CASE

with null_table as (select null as null_set from dual )
select 
     case null_set
     when  (null) then 'NULL INDEED'
     else 'NOTNULL?'
     end as AM_I_NULL_OR_NOT   
from null_table

The Searched CASE evaluates null_set as expected, yet, Simple CASE appears not to do so.

Questions:
How do I perform a Simple CASE evaluation on null_set ?

Why does the Simple CASE evaluate as it does?

Answer 1

In Oracle, null cannot be compared against using the = operator.

For example:

select * from dual where null = null; -- No result
select * from dual where 1 = 1; -- gives a result

So what you can do is use NVL to replace null by another value :

with null_table as (select null as null_set from dual )
select 
     case nvl(null_set,'X')
     when  'X' then 'NULL INDEED'
     else 'NOTNULL?'
     end as AM_I_NULL_OR_NOT   
from null_table

(make sure your field can never be equal to the value, X in the example.)