Oracle分组函数之ROLLUP用法

rollup函数 本博客简单介绍一下oracle分组函数之rollup的用法，rollup函数常用于分组统计，也是属于oracle分析函数的一种

环境准备

create table dept as select * from scott.dept;
create table emp as select * from scott.emp;

业务场景：求各部门的工资总和及其所有部门的工资总和

这里可以用union来做，先按部门统计工资之和，然后在统计全部部门的工资之和

select a.dname, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by a.dname
union all
select null, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno;

上面是用union来做，然后用rollup来做，语法更简单，而且性能更好

select a.dname, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by rollup(a.dname);

业务场景：基于上面的统计，再加需求，现在要看看每个部门岗位对应的工资之和

select a.dname, b.job, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by a.dname, b.job
union all//各部门的工资之和
select a.dname, null, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by a.dname
union all//所有部门工资之和
select null, null, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno;

用rollup实现，语法更简单

select a.dname, b.job, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by rollup(a.dname, b.job);

假如再加个时间统计的，可以用下面sql：

select to_char(b.hiredate, 'yyyy') hiredate, a.dname, b.job, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by rollup(to_char(b.hiredate, 'yyyy'), a.dname, b.job);

cube函数

select a.dname, b.job, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by cube(a.dname, b.job);

cube函数是维度更细的统计，语法和rollup类似

假设有n个维度，那么rollup会有n个聚合，cube会有2n个聚合

rollup统计列 rollup(a,b) 统计列包含：(a,b)、(a)、() rollup(a,b,c) 统计列包含：(a,b,c)、(a,b)、(a)、() …