Oracle 高级查询
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1 集合运算
union 并集 把两张表合成一张表
intersect 交集 一样的留下，不一样的不要
minus 减去 前面的结果减去后面的结果
create table emp3 as select * from emp2 where deptno=20; create table emp4 as select * from emp2 where deptno=30; alter table emp3 rename to emp20; alter table emp4 rename to emp30; select * from emp20; select * from emp30; select * from emp20 union select * from emp30; select * from emp30 intersect select * from emp2; select * from emp2 minus select * from emp30;
2 connect by 和start with
依托于该语法，我们可以将一个表形结构的以树的顺序列出来
提供一个伪列 level
level
找到头 select ename from emp2 where mgr is null; select empno,ename,mgr from emp start with ename='KING' connect by prior empno=mgr; select level,empno,ename,mgr from emp start with ename=(select ename from emp2 where mgr is null) connect by prior empno=mgr; select * from (select level lv,empno,ename,mgr from emp start with ename=(select ename from emp2 where mgr is null) connect by prior empno=mgr) where lv=2;
3高级分组函数
rollup 函数 小计
rollup 函数多一行 小计
对于分组的列为null
对于聚集函数为求 小计
select job,sum(sal) from emp GROUP BY rollup(job); select job,sum(sal),round(avg(sal)),max(sal),count(empno)from emp group by rollup(job);
统计rollup(x,y) 统计第一个x 不统计y
select dname,job,sum(sal) from emp inner join dept using(deptno) group by rollup(dname,job);
cube 统计所有的列
select dname,job,sum(sal) from emp inner join dept using(deptno) froup by cube(dname,job) order by dname;
rollup 和cube 就是汇总的结果
grouping 和grouping sets
select grouping(dname),dname ,grouping(job),job,sum(sal) from emp inner join dept using(deptno) group by rollup(dname,job) order by dname;
select * from (select grouping(dname),dname ,grouping(job) N,job,sum(sal) from emp inner join dept using(deptno) group by rollup(dname,job) order by dname) where dname='SALES' and N=1 ;
select grouping(dname),dname,grouping(job),job,sum(sal) from emp inner join dept using(deptno) group by cube(dname,job) order by dname;
只查询汇总的行 总的汇总也不要
select dname,job,sum(sal) from emp inner join dept using(deptno) group by grouping sets(dname,job);
如果需要查询的结果只有小计 可以用cube 和 grouping sets 用grouping sets 的效率高于cube 和rollup
排名函数
既能排序又能排名
rank() over( orader by xx)
重复就会削去下一个编号
select rank() over(order by sal desc),ename,sal from emp;
dense_rank() over(orader by xx)
重复不削去编号
select dense_rank() over(order by sal desc),ename,sal from emp;
先排序在rownum 比rownum 简单
select row_number() over(order by sal desc),ename from emp;
