008 内连接练习 其他连接

/*
时间：2020/09/11
功能：
    一 练习题
    二 其他连接
*/   

一 练习题

-- 查询: 员工姓名、工资、工资等级
select "E".ename, "E".sal, "S".grade
    from emp "E"
    join salgrade "S"
    on "E".sal between "S".losal and "S".hisal

-- 查询: 员工姓名第二个字母为A、
-- 输出: 员工姓名、工资、部门编号、部门名称、工资等级
select "E".ename, "E".sal, "E".deptno, "D".dname, "S".grade
    from emp "E"
    join dept "D"
    on "E".deptno = "D".deptno
    join salgrade "S"
    on "E".sal between "S".losal and "S".hisal
    where "E".ename like '_a%'

-- 每个员工姓名、部门编号、部门名称、薪水、薪水等级
select "E".ename, "E".deptno, "D".dname, "E".sal, "S".grade
    from emp "E"
    join dept "D"
    on "E".deptno = "D".deptno
    join salgrade "S"
    on "E".sal between "S".losal and "S".hisal

-- 查找每个部门的编号 该部门所有员工的平均工资 平均工资的等级
-- 写法一
select "T".deptno, "T"."dept_avg(sal)", "S".grade
    from salgrade "S"
    join(
        select deptno, avg(sal) "dept_avg(sal)"
            from emp 
            group by deptno) "T"
    on "S".losal <= "T"."dept_avg(sal)" and "S".hisal >= "T"."dept_avg(sal)"
    
-- 写法二
select "T".deptno, "T"."dept_avg(sal)", "S".grade
    from 
        (select deptno, avg(sal) "dept_avg(sal)"
            from emp
            group by deptno) "T"
    join salgrade "S"
    on "T"."dept_avg(sal)" between "S".losal and "S".hisal

-- 写法三
select "T".deptno, "T"."dept_avg(sal)", "S".grade
    from 
        (select deptno, avg(sal) "dept_avg(sal)"
            from emp
            group by deptno) "T", salgrade "S"
    where "T"."dept_avg(sal)" between "S".losal and "S".hisal

-- 查找每个部门的编号 部门名称 该部门所有员工的平均工资 平均工资的等级
select "T".deptno, "D".dname, "T"."dept_avg(sal)", "S".grade
    from
        (select deptno, avg(sal) "dept_avg(sal)"
        from emp 
        group by deptno) "T"
    join dept "D"
    on "T".deptno = "D".deptno
    join salgrade "S"
    on "T"."dept_avg(sal)" between "S".losal and "S".hisal

-- 求出emp表中所有领导的信息 
select * 
    from emp
    where empno in 
    ( select mgr
        from emp)

-- 求出emp表中所有非领导的信息
select * 
    from emp
    where empno not in 
    ( select isnull(mgr, 0)
        from emp)

-- 求出平均薪水最高的部门的编号和部门的平均工资
-- 方法一
select top 1 deptno, avg(sal)
    from emp
    group by deptno
    order by avg(sal) desc

-- 方法二
select *
    from (
            select deptno, avg(sal) "avg_sal"
                from emp
                group by deptno
            )"E"
    where "E"."avg_sal" = 
(
    select max("avg_sal") from
        (select deptno, avg(sal) "avg_sal" 
            from emp 
            group by deptno) "T"
)

-- 有一个人工资最低 把这个人排除掉
-- 剩下的人中工资最低的前3个人的姓名 工资 部门编号 部门名称 工资等级 输出    
select top 3 "T".ename, "T".sal, "T".deptno, "D".dname, "S".grade
    from(
        select * 
            from emp "E"
            where sal > (select min(sal) from emp)) "T"
    join dept "D"
    on "T".deptno = "D".deptno
    join salgrade "S"
    on "T".sal between "S".losal and "S".hisal
    order by "T".sal

二 其他连接

-- 外连接
-- 左外连接
select * 
    from dept "D"
    left join emp "E"
    on "D".deptno = "E".deptno

-- 右外连接
select * 
    from emp "E" 
    right join dept "D"
    on "D".deptno = "E".deptno


-- 完全连接
select * 
    from dept 
    full join emp 
    on dept.deptno = emp.deptno

-- 交叉连接
select * 
    from emp 
    cross join dept    -- 等价于 select * from emp, dept


-- 自连接
-- 把最高工资人的信息输出, 不准用聚合函数。
select * 
    from emp
    where empno not in(
        select distinct "E1".empno
            from emp "E1"
            join emp "E2"
            on "E1".sal < "E2".sal
            )


-- 联合
-- 输出每个员工姓名 工资 上司姓名
select "E1".ename, "E1".sal, "E2".ename "Boss name"
    from emp "E1"
    join emp "E2"
    on "E1".mgr = "E2".empno -- 第一步: 求上司姓名
    union
    select ename, sal, '最大老板'
    from emp
    where mgr is null