rollup函數(shù)
本博客簡(jiǎn)單介紹一下oracle分組函數(shù)之rollup的用法，rollup函數(shù)常用于分組統(tǒng)計(jì)，也是屬于oracle分析函數(shù)的一種
環(huán)境準(zhǔn)備
create table dept as select * from scott.dept;
create table emp as select * from scott.emp;
業(yè)務(wù)場(chǎng)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(tǒng)計(jì)工資之和，然后在統(tǒng)計(jì)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(jiǎn)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(yè)務(wù)場(chǎng)景：基于上面的統(tǒng)計(jì)，再加需求，現(xiàn)在要看看每個(gè)部門崗位對(duì)應(yīng)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(shí)現(xiàn)，語法更簡(jiǎn)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(gè)時(shí)間統(tǒng)計(jì)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(shù)
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(shù)是維度更細(xì)的統(tǒng)計(jì)，語法和rollup類似
假設(shè)有n個(gè)維度，那么rollup會(huì)有n個(gè)聚合，cube會(huì)有2n個(gè)聚合
rollup統(tǒng)計(jì)列
rollup(a,b) 統(tǒng)計(jì)列包含：(a,b)、(a)、()
rollup(a,b,c) 統(tǒng)計(jì)列包含：(a,b,c)、(a,b)、(a)、()
....
cube統(tǒng)計(jì)列
cube(a,b) 統(tǒng)計(jì)列包含：(a,b)、(a)、(b)、()
cube(a,b,c) 統(tǒng)計(jì)列包含：(a,b,c)、(a,b)、(a,c)、(b,c)、(a)、(b)、(c)、()
....
總結(jié)
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