MySQL练习题

-- 借助于emp表和dept表
-- 注意：快捷键出现的函数如：`REPLACE`(str,from_str,to_str)，有``会引起错误


-- 1.找出各月倒数第3天受雇的所有员工.
SELECT
    ENAME,
    HIREDATE,
    LAST_DAY(HIREDATE) MOBTH_LAST
FROM
    EMP
WHERE
    HIREDATE = LAST_DAY(HIREDATE) - 2;

-- 2.找出早于39年前受雇的员工.
SELECT
    *
FROM
    EMP
WHERE
    TO_DAYS(HIREDATE) < TO_DAYS(
        date_format(now(), '%Y-%m-%d')
    ) - 39 * 365;

-- 3.以首字母大写的方式显示所有员工的姓名.
SELECT
    CONCAT(
        UPPER(SUBSTR(ENAME, 1, 1)),
        LOWER(SUBSTR(ENAME FROM 2))
    )
FROM
    EMP;

-- 4.显示正好为5个字符的员工的姓名.
SELECT
    ENAME
FROM
    EMP
WHERE
    LENGTH(ENAME) = 5;

-- 5.显示不带有"R"的员工的姓名
CREATE TABLE TEMP LIKE EMP;

INSERT INTO TEMP SELECT
    *
FROM
    EMP;

DELETE
FROM
    TEMP
WHERE
    ENAME LIKE '%R%';

SELECT
    ENAME
FROM
    TEMP;

DROP TABLE TEMP;

-- 6.显示所有员工姓名的前三个字符.
SELECT
    SUBSTR(ENAME FROM 1 FOR 3)
FROM
    EMP;

-- 7.显示所有员工的姓名,用a替换所有"A"
SELECT
    REPLACE (ENAME, 'A', 'a')
FROM
    EMP;

-- 8.显示满10年服务年限的员工的姓名和受雇日期.:SELECT
SELECT
    ENAME,
    HIREDATE
FROM
    EMP
WHERE
    TO_DAYS(HIREDATE) < TO_DAYS(
        date_format(now(), '%Y-%m-%d')
    ) - 10 * 365;

-- 9.显示员工的详细资料,按姓名排序.
SELECT
    *
FROM
    EMP
ORDER BY
    ENAME;

-- 10.显示员工的姓名和受雇日期,根据其服务年限,将最老的员工排在最前面.
SELECT
    ENAME,
    HIREDATE
FROM
    EMP
WHERE
    TO_DAYS(HIREDATE) < TO_DAYS(
        date_format(now(), '%Y-%m-%d')
    ) - 10 * 365
ORDER BY
    HIREDATE;

-- 11.显示所有员工的姓名、工作和薪金,按工作的降序排序,若工作相同则按薪金排序.
SELECT
    ENAME,
    JOB,
    SAL
FROM
    EMP
ORDER BY
    JOB DESC,
    SAL ASC;

-- 12.显示所有员工的姓名、加入公司的年份和月份,按受雇日期所在月排序,若月份相同则将最早年份的员工排在最前面.
SELECT ENAME,YEAR(HIREDATE) '年份',MONTH(HIREDATE)'月份' FROM EMP ORDER BY
MONTH(HIREDATE),HIREDATE;
-- --13.取得每个部门最高薪水的人员名称
SELECT
    E.ENAME,
    T.*
FROM
    EMP E
JOIN (
    SELECT
        DEPTNO,
        MAX(SAL) AS MAXSAL
    FROM
        EMP
    GROUP BY
        DEPTNO
) T ON T.DEPTNO = E.DEPTNO
AND T.MAXSAL = E.SAL;

-- 14.找出在(任何年份的)2月受聘的所有员工。
SELECT
    *
FROM
    EMP
WHERE
    MONTH (HIREDATE) = 2;

-- 15.对于每个员工,显示其加入公司的天数.
SELECT
    ENAME,
    TO_DAYS(HIREDATE) AS 入职天数
FROM
    EMP;

-- 16.显示姓名字段的任何位置包含"A"的所有员工的姓名.
SELECT
    ENAME
FROM
    EMP
WHERE
    ENAME LIKE '%A%';

-- 17.列出所有job=‘CLERK’ 的员工平均薪资
SELECT
    ENAME,
    AVG(SAL)
FROM
    EMP
WHERE
    JOB = 'CLERK';

-- 18.列出job=‘CLERK’员工的平均薪资 按照部门分组 
SELECT
    DEPTNO,
    DNAME,
    AVG(SAL)
FROM
    (
        SELECT
            A.DEPTNO,
            DNAME,
            A.ENAME,
            SAL
        FROM
            (
                SELECT
                    *
                FROM
                    EMP
                WHERE
                    JOB = 'CLERK'
            ) A
        INNER JOIN DEPT B ON A.DEPTNO = B.DEPTNO
    ) C
GROUP BY
    DNAME;

-- 19.列出job=‘CLERK’员工的平均薪资 按照部门分组 并且部门编号 in(10,30) 按照平均薪资 降序排列
SELECT
    DEPTNO,
    DNAME,
    AVG(SAL)
FROM
    (
        SELECT
            A.DEPTNO,
            DNAME,
            A.ENAME,
            SAL
        FROM
            (
                SELECT
                    *
                FROM
                    EMP
                WHERE
                    JOB = 'CLERK'
            ) A
        INNER JOIN DEPT B ON A.DEPTNO = B.DEPTNO
    ) C
WHERE
    DEPTNO IN (10, 30)
GROUP BY
    DNAME
ORDER BY
    AVG(SAL) DESC;

-- 20.列出job=‘CLERK’员工的平均薪资 按照部门分组 并且部门编号 in(20,30) 并且部门员工数量>=2人 按照平均薪资 降序排列
SELECT
    *
FROM
    (
        SELECT
            DEPTNO,
            DNAME,
            AVG(SAL),
            COUNT(ENAME) AS CO
        FROM
            (
                SELECT
                    A.DEPTNO,
                    DNAME,
                    A.ENAME,
                    SAL
                FROM
                    (
                        SELECT
                            *
                        FROM
                            EMP
                        WHERE
                            JOB = 'CLERK'
                    ) A
                INNER JOIN DEPT B ON A.DEPTNO = B.DEPTNO
            ) C
        WHERE
            DEPTNO IN (20, 30)
        GROUP BY
            DNAME
        ORDER BY
            AVG(SAL) DESC
    ) AS D
WHERE
    CO >= 2;