Java39: 数据库三(Oracle)

Oracle 高级查询

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;