SQL server内连接查询
内连接
select top*from A
join B
on...
join C
on...
where...
group by...
having...
order by...
1.//在scott表中查询员工名字中不包含A的所有员工，前三名员工的姓名，工资，工资等级，部门名字
select top 3 "E".ename,"E".sal,"S".grade,"D".dname
from emp "E"
join dept "D" on "E".deptno="D".deptno
join salgrade "S" on "E".sal>=losal and "E".sal<=hisal //或on "E".sal between "S".losal and "S".hisal
where "E".ename not like '%A%' //注意这句话要放在最后
order by "E".sal desc //注意这句话要放在最后
2.//在scott表中查找每个部门编号，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,"T".avg_sal "部门员工平均工资","S".grade "工资等级","D".dname "部门名称"
from(
select deptno,avg(sal)as "avg_sal" //将查询结果当作临时表
from emp
group by deptno
) "T"
join salgrade "S"
on "T".avg_sal between "S".losal and "S".hisal
join dept "D"
on "T".deptno="D".deptno
等价于以下写法（join 前后 两个部分互换）
select "T".deptno,"T".avg_sal "部门员工平均工资","S".grade "工资等级","D".dname "部门名称"
from salgrade "S"
join (
select deptno,avg(sal)as "avg_sal"
from emp
group by deptno
) "T" /将查询结果当作临时表
on "T".avg_sal between "S".losal and "S".hisal
join dept "D"
on "T".deptno="D".deptno
3.// 查询平均薪水最高的部门名称，编号，工资
select "T".avg_sal, "T".deptno,"D".dname
from
(select top 1 avg(sal)"avg_sal",deptno from emp group by deptno order by deptno) "T" 将查询结果当作临时表
join dept "D" on "T".deptno="D".deptno
4.//排除最低工资的员工后，查询剩下员工中工资最低的3位员工的姓名，工资，部门编号，部门名称，工资等级。
select top 3 "T".ename "姓名","T".sal "工资","T".deptno "部门编号","D".dname "部门名称","S".grade "工资等级"
from (select * from emp where sal>(select min(sal) from emp) ) "T" /将查询结果当作临时表
join dept "D"on("T".deptno="D".deptno)
join salgrade "S"on("T".sal between "S".losal and "S".hisal )
order by "T".sal ///注意这句话要放在最后
5
select * from emp
join dept
on emp.deptno=dept.deptno and emp.sal>2000 //on中即可以写连接条件与可以写过滤条件
等价于：
select * from emp //将查询对象互换
join dept
on emp.deptno=dept.deptno and emp.sal>2000 //on中即可以写连接条件与可以写过滤条件
等价于：
select * from emp
join dept
on emp.deptno=dept.deptno
where emp.sal>2000 //where连接条件
等价于：
select * from emp
join dept
on emp.sal>2000
where emp.deptno=dept.deptno //将两条件互换
6.查询基本模式
select top*
from A
join B
on...
join C
on...
where...
group by...
having...
order by...
例：把工资大于1500的所有员工按部门分组，把部门平均工资大于2000的最高前2个的部门的编号，部门的名称，部门平均工资 的等级输出
select "T".*,"D".dname, "S".grade
from dept "D"
join(
select top 2 "E".deptno,avg("E".sal) "avg_sal"
from emp "E"
join dept "D" on "E".deptno="D".deptno
join salgrade "S" on "E".sal between "S".losal and "S".hisal //这两句不要，也两样可行。
where "E".sal>1500
group by "E".deptno
having avg("E".sal)>2000
order by "avg_sal" desc
)"T" //当作临时表
on "T".deptno="D".deptno
join salgrade "S"
on "T".avg_sal
between "S".losal and "S".hisal