How to conditionally add an AND condition to a WHERE clause in SQL Server

Question

I have a table with the following schema:

| ID | BUNDLE_ID | IS_ADMIN |

I need to select data from the above table having an AND clause on the basis of certain criteria, i.e

IF @FLAG = 1
    SELECT * 
    FROM TABLE A 
    WHERE A.IS_ADMIN = 1 AND BUNDLE_ID IN (3, 5)
ELSE
    SELECT * 
    FROM TABLE A 
    WHERE A.IS_ADMIN = 1 AND BUNDLE_ID IN (1, 2)

Can I achieve this in a single query?

Answer 1

General approach is to rewrite the query with a boolean expression that evaluates to what you need based on flag's value:

SELECT * FROM TABLE A WHERE A.IS_ADMIN = 1 AND ( -- Common part ...
    (@Flag=1  AND BUNDLE_ID IN(3,5))     -- IF   ...
OR
    (@Flag<>1 AND BUNDLE_ID IN(1,2))     -- ELSE ...
)