Question

Here’s my queries, they don’t work but I want to do something like this :

SELECT a_field FROM a_table
WHERE
... 
AND
CASE
WHEN a_value_from_another_query IS NULL THEN a_second_field IS NULL
ELSE a_second_field = a_value_from_another_query
END

Or

SELECT a_field FROM a_table
WHERE
... 
AND
CASE a_value_from_another_query
WHEN NULL THEN a_second_field IS NULL
ELSE a_second_field = a_value_from_another_query
END

Or

SELECT a_field FROM a_table
WHERE
... 
AND
CASE NVL(a_value_from_another_query, 'x')
WHEN 'x' THEN a_second_field IS NULL
ELSE a_second_field = a_value_from_another_query
END

When a_value_from_another_query IS NULL, I want to add a_second_field IS NULL to my WHERE clause, when a_value_from_another_query IS NOT NULL, I want to add a_second_field = a_value_from_another_query to my WHERE clause. How can I achieve this ?

Answer 1

Sounds like you simply picked up the wrong tool from the toolbox.

Unless I have horribly misunderstood you, the following:

WHERE
    (a_value_from_another_query IS NULL AND a_second_field IS NULL)
  OR
    (a_value_from_another_query IS NOT NULL AND a_second_field = a_value_from_another_query)

… should so what you want.