SQL CASE WHEN statement

SQL CASE WHEN statement:

SELECT
    s.school_id,
    s. NAME,
    s.school_type,
    (
        CASE s.school_type
        WHEN 3 THEN
            'aa'
        WHEN 2 THEN
            'bb'
        END
    ) 自定义
FROM
    franchised_school_info s