Using case expression inside where clause

Question

what I wanted is to add another condition using case statement or something.

I tried:

SELECT * FROM tblcust 
WHERE cust_id = :p_cust_id 
CASE WHEN :p_first_name IS NOT NULL THEN
        AND first_name = :p_first_name
     WHEN :p_last_name IS NOT NULL THEN
        AND last_name = :p_last_name
     WHEN :p_first_name IS NULL AND :p_last_name IS NULL THEN
        NULL
     END;

Answer 1

You may not be able to use a CASE expression here to represent your logic, but it can certainly be reworded:

SELECT * FROM tblcust 
WHERE
    cust_id = :p_cust_id AND
    ((:p_first_name IS NOT NULL AND first_name = :p_first_name) OR
     (:p_last_name IS NOT NULL AND last_name = :p_last_name)    OR
     (:p_first_name IS NULL AND :p_last_name IS NULL));

But this is ugly, and we might able to use a COALESCE trick here to make it simpler:

SELECT * FROM tblcust 
WHERE
    cust_id = :p_cust_id AND
    (COALESCE(:p_first_name, first_name || ' ') = first_name) OR
     COALESCE(:p_last_name, last_name || ' ') = last_name) OR
     (:p_first_name IS NULL AND :p_last_name IS NULL));

The reason your CASE expression is structured incorrectly is because you are making it generate logical expressions , when it is only allowed to generate values . But, in this case, we don't even need a CASE expression to handle your logic.

Answer 2

I am not sure what you want logically , but you can do case inside a case like

With a 
as (
Select 1 id , NULL col1 union all
Select 2,10 union all
Select 3,Null
)
Select * from a
where id =1
OR  Case When col1 is not null then id=2
End

Answer 3

To make theses "mutually exclusive" sets of conditons use parentheses plus OR

SELECT * FROM tblcust 
WHERE (:p_first_name IS NOT NULL AND first_name = :p_first_name) 
OR (:p_last_name IS NOT NULL AND last_name = :p_last_name)
OR (:p_FIRST_name IS NULL AND :p_last_name IS NULL AND cust_id = :p_cust_id)

If there are still more conditions to add the be careful to contain all the sets within an "catch all" pair of parentheses