Oracle分組函數之ROLLUP用法

rollup函數
本博客簡單介紹一下oracle分組函數之rollup的用法，rollup函數常用於分組統計，也是屬於oracle分析函數的一種

環境准備

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

業務場景：求各部門的工資總和及其所有部門的工資總和

這里可以用union來做，先按部門統計工資之和，然后在統計全部部門的工資之和

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來做，然后用rollup來做，語法更簡單，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);

業務場景：基於上面的統計，再加需求，現在要看看每個部門崗位對應的工資之和

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//各部門的工資之和
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//所有部門工資之和
select null, null, sum(b.sal)
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno;

用rollup實現，語法更簡單

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);

假如再加個時間統計的，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函數

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函數是維度更細的統計，語法和rollup類似

假設有n個維度，那么rollup會有n個聚合，cube會有2n個聚合

• rollup統計列
  rollup(a,b) 統計列包含：(a,b)、(a)、()
  rollup(a,b,c) 統計列包含：(a,b,c)、(a,b)、(a)、()
  ....

• cube統計列
  cube(a,b) 統計列包含：(a,b)、(a)、(b)、()
  cube(a,b,c) 統計列包含：(a,b,c)、(a,b)、(a,c)、(b,c)、(a)、(b)、(c)、()
  ....