Oracle-子查询
一、WHERE条件中的子查询
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1. 比black工资高的雇员有哪些?
select ename
from emp
where sal>(select sal from emp where ename='BLAKE');
2. 高于30部门最高工资的雇员有哪些?
select ename,sal
from emp
where sal>(select max(sal) from emp where deptno=30);
select ename,sal
from emp
where sal > all (select sal from emp where deptno=10); --任何
3. 当all后面接子查询的时候
"x = ALL (...)": The value must match all the values in the list to evaluate to TRUE.所有值都要匹配
"x != ALL (...)": The value must not match any values in the list to evaluate to TRUE.至少有一个值不匹配
"x > ALL (...)": The value must be greater than the biggest value in the list to evaluate to TRUE.大于最大的值
"x < ALL (...)": The value must be smaller than the smallest value in the list to evaluate to TRUE.小于最小的值
"x >= ALL (...)": The value must be greater than or equal to the biggest value in the list to evaluate to TRUE.大于等于最大的值
"x <= ALL (...)": The value must be smaller than or equal to the smallest value in the list to evaluate to TRUE.小于等于最小的值
4. 大于10部门最小工资的雇员有哪些?
select ename,sal
from emp
where sal> (select min(sal) from emp where deptno=10);
select ename,sal
from emp
where sal > any (select sal from emp where deptno=10); --any 大于任何一个，那不就是最小的么？？,任意一个
5. 当any后面接子查询的时候
"x = ANY (...)": The value must match one or more values in the list to evaluate to TRUE.至少匹配一个值
"x != ANY (...)": The value must not match one or more values in the list to evaluate to TRUE.一个值都不匹配
"x > ANY (...)": The value must be greater than the smallest value in the list to evaluate to TRUE.大于最小值
"x < ANY (...)": The value must be smaller than the biggest value in the list to evaluate to TRUE.小于最大值
"x >= ANY (...)": The value must be greater than or equal to the smallest value in the list to evaluate to TRUE.大于等于最小值
"x <= ANY (...)": The value must be smaller than or equal to the biggest value in the list to evaluate to TRUE.小于等于最大值
6. 工资最高的人是谁?
select ename from emp
where sal=(select max(sal) from emp);
7. 和ALLEN同部门，工资高于MARTIN的雇员有哪些?
select ename from emp
where deptno=(select deptno from emp where ename='ALLEN')
and sal>(select sal from emp where ename='MARTIN');
8. 工作和部门与SMITH相同，工资高于JAMES的雇员有哪些?
select ename from emp
where (job,deptno)=(select job,deptno from emp where ename='SMITH')
and sal>(select sal from emp where ename='JAMES');
二、FROM子句中的子查询
1. 工资高于本部门平均工资的人（拿上游工资的人）有哪些？
①求出每个部门的平均工资，把这个作为一张表
②使用emp表和平均工资表进行关联，
select ename,sal,avgsal,e.deptno
from emp e,
(select avg(sal) avgsal,deptno
from emp
group by deptno) b
where e.deptno=b.deptno
and e.sal>b.avgsal;
三、伪列：rownum
特点：先有结果集在有rownum，是对结果集的一个编号
1. 工资前五名的人?(TOP-N 分析)
①先把工资排序
②在使用rownum限结果集（为什么不在第一步就使用rownum限定结果集？执行顺序的问题，where要比order by先执行，获取rownum<6的时候还没来得及排序在从emp里面拿出来
select ename,sal
from emp
where sal in
(select sal
from (select distinct sal from emp order by sal desc)
where rownum<6)
order by sal desc;
3. 工资6~10的人?
①先把工资排序
②把工资排名在6~10的拿出来，由于不能使用rownum>6 and xxx<10这样，所以要加一步，把rownum变成id列，这样就又构造成一个结果集
③把上一个结果集中id为6~10的条目拿出来
④和emp关联
select ename,sal from emp
where sal in
(select sal from
(select rownum rn,sal
from (select distinct sal
from emp order by sal desc))
where rn between 6 and 10)
order by sal desc;
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