sql数据库查询相关操作，SQL的应用——SQL多表连查、子查询、多行子查询

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1	**SQL多表连查**

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--查询员工和部门信息 select * from emp e,dept d where e.deptno=d.deptno --查询员工姓名，部门名称 select e.ename,d.dname from emp e,dept d where e.deptno = d.deptno --查询所有员工姓名，部门名称 select e.*, d.dname from emp e,dept d where e.deptno=d.deptno --查询工资大于3000的员工姓名，工资和部门名称 select e.ename,e.sal,d.dname from emp e,dept d where e.deptno=d.deptno and e.sal>=3000

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--非等值查询 --查询公司工资等级 select * from emp e,salgrands where e.sal<=s.hisal and e.sal>s.losal select * from salagrade

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--外链接 --左外连接 select*from emp e,dept d where e.deptno=d.deptno(+) --右外连接 select*from emp e,dept d where e.deptno(+)=d.deptno

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--自连接 --查询员工姓名和经理姓名 select e1.ename ,e2.ename from emp e1,emp e2 where e1.mgr=e2.deptno --查询员工姓名、经理姓名和其他经理姓名 select e1.ename,e2.ename,e3.ename from emp e1,emp e2, emp e3 where e1.mgr=e2.empno and e2.empno=e3.empno

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1	**以上为92版仅在面试出现**

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--SQL99   表连接 --交叉连接   cross join select *from emp e cross join dept d --自然连接      natural join select *from emp natural join dept --using select e.ename,deptno from emp e join dept d using(deptno) --on 自定义连接 select *from emp e join dept d on e.deptno=d.deptno select *from emp e1 join emp e2 on e1.mgr=e2.empno --查询员工的姓名、经理及其经理的名字 select e1.ename,e2.ename,e3.ename from emp e1 join emp e2 on e1.mgr=e2.empno join emp e3 on e2.mgr=e3.empno --SQL99  inner join  两边都合法的数据 select*from emp e inner join dept d on e.deptno=d.deptno --left join 以左表为主 select*from emp e left join dept d on e.deptno=d.deptno --right join 以右表为主 select*from emp e right join dept d on e.deptno=d.deptno --full join 全连 取两个表的所有数据 select*from emp e full join dept d on e.deptno=d.deptno ----查询员工的姓名、经理及其经理的名字和部门名字 select e1.ename, d.dname, e2.ename, d2.dname   from emp e1   left join dept d     on e1.deptno = d.deptno   left join emp e2     on e2.mgr = e2.empno   left join dept d2     on d2.deptno = d2.deptno

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**子查询**

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--比CLARK工资高的人 select SAL from emp where ename='CLARK' select *from emp where sal>(select SAL from emp where ename='CLARK') --查询工资高于平均工资的雇员姓名和工资 select avg(sal) from emp select ename,sal from emp where sal>(select avg(sal) from emp ) --查询同SCOTT同部门的且工资比他低的员工的名字和工资 select deptno from emp where ename='SCOTT' select sal from emp where ename='SCOTT' select ename, sal   from emp  where deptno = (select deptno from emp where ename = 'SCOTT')    and sal < (select sal from emp where ename = 'SCOTT') --查询和'SMITH','SCOTT','CLARK'同一个部门的员工姓名 select distinct deptno from emp where ename in('SMITH','SCOTT','CLARK') select *   from emp  where deptno in (select distinct deptno                     from emp                    where ename in ('SMITH', 'SCOTT', 'CLARK')) --查询和'SMITH', 'SCOTT', 'CLARK'同一个部门并不包含他们三个的员工姓名    and ename not in ('SMITH', 'SCOTT', 'CLARK') --查询工资最高的员工名字和工资 select ename,sal from emp where sal=(select max(sal)from emp ) --查询职务和'SCOTT'相同但是比'SCOTT'雇佣时间早的雇员信息 select * from emp  where job = (select job from emp where ename = 'SCOTT')    and hiredate < (select hiredate from emp where ename = 'SCOTT') --查询工资比'SCOTT'高或者雇佣时间比'SCOTT'早的雇员编号和姓名 select empno,ename from emp  where job = (select job from emp where ename = 'SCOTT')    and hiredate < (select hiredate from emp where ename = 'SCOTT')

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**多行子查询**

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--查询工资低于任何一个“CLERK”的工资的雇员信息 select*from emp where sal all (select sal from emp where job = 'SALESMAN') --查询部门20中职务同部门10的雇员一样的雇员信息。 select *from emp where job in (select job from emp where deptno=10)and deptno=20 --查询在雇员中有哪些人是经理人 select *   from emp  where empno in (select distinct mgr                    from emp                   where mgr is not null                      or mgr != '') --找出部门编号为20的所有员工中收入最高的职员 select ename   from emp  where sal = (select max(sal) from emp where deptno = 20)    and deptno = 20 </any(select>