Compare 1 field from sub query against other?

Question

I am trying to compare two fields in oracle select query as part of case statement one of which is coming from sub query but I get error.

Eg

select 1 as one, 
       (select 2 from dual) as two,
       case when one=two then 'EQUAL'
            else 'NOTEQUAL'
       end match
from dual;

Error ORA-00904: TWO invalid identifier

Thoughts how can rewrite this?

Thanks in advance!

Answer 1

You cant use the alias, so you have to rewrite the data source and subquery.

SELECT 1 as one,
       (SELECT 2 FROM dual) as two,
       CASE WHEN 1 = (SELECT 2 FROM dual)
            THEN 'EQUAL'
            ELSE 'NOTEQUAL' 
        END match
  FROM dual

Result

one two match
1   2   NOTEQUAL

Answer 2

The problem is you cant use the alias on the same level, you need to do a subquery or a cte

WITH step1 as (
    select 1 as one
    from dual
), step2 as (
    select 2 as two
    from dual
)
SELECT case when one=two then 'EQUAL'
            else 'NOTEQUAL'
       end match
FROM step1
CROSS JOIN step2

Answer 3

Use a simple subquery

Select t.*,
       case when one=two then 'EQUAL'
            else 'NOTEQUAL'
       end match
From (
    select 1 as one, 
           (select 2 from dual) as two
    from dual
) t;