특수 Query

-- CASE DECODE = SWITCH

--1번
SELECT employee_id, first_name, phone_number,
    CASE SUBSTR(phone_number, 1, 3)
        WHEN '515' THEN '서울'
        WHEN '590' THEN '부산'
        WHEN '659' THEN '광주'
        WHEN '603' THEN '대전'
        ELSE '기타'
    END AS "지역"
FROM employees;

--2번
SELECT employee_id, first_name, phone_number,
    CASE
        WHEN SUBSTR(phone_number,1,3) = '515' THEN '서울'
        WHEN SUBSTR(phone_number,1,3) = '590' THEN '부산'
        WHEN SUBSTR(phone_number,1,3) = '659' THEN '광주'
        WHEN SUBSTR(phone_number,1,3) = '603' THEN '대전'
        ELSE '기타'
    END AS "지역"
FROM employees;

--DECODE
SELECT employee_id, first_name, phone_number,
    DECODE( SUBSTR( phone_number,1,3),
        '515','서울',
        '590','부산',
        '659','광주',
        '603','대전',
        '기타')
FROM employees;