MySQL 中的嵌套 CASE 语句

MySQL中的嵌套CASE语句

sql
CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ...
    ELSE result
END

sql
SELECT id, name,
    CASE
        WHEN age < 18 THEN '未成年'
        WHEN age >= 18 AND age < 60 THEN '成年人'
        ELSE '老年人'
    END AS age_group
FROM users;

sql
SELECT id, name,
    CASE
        WHEN score >= 90 THEN '优秀'
        WHEN score >= 80 AND score < 90 THEN '良好'
        WHEN score >= 70 AND score < 80 THEN '中等'
        WHEN score >= 60 AND score < 70 THEN '及格'
        ELSE '不及格'
    END AS grade
FROM students;

sql
SELECT id, name,
    CASE
        WHEN gender = '男' THEN
            CASE
                WHEN age < 18 THEN '男孩'
                WHEN age >= 18 AND age < 60 THEN '男士'
                ELSE '老先生'
            END
        WHEN gender = '女' THEN
            CASE
                WHEN age < 18 THEN '女孩'
                WHEN age >= 18 AND age < 60 THEN '女士'
                ELSE '老太太'
            END
        ELSE '未知'
    END AS gender_group
FROM users;