Example (MySQL):
SELECT
-- this CASE may be replaced by COALESCE
CASE
WHEN C1 IS NOT NULL THEN C1
ELSE 0
END
FROM dual;
In the example, the CASE statement can be replaced with SELECT COALESCE(C1, 0) that produces the same output.
If you prefer using CASE expressions, select the Prefer CASE expressions over COALESCE function option on the inspection page.