select deptno,stddev(sal) from emp group by deptno;

variance 返回一组值的方差差

select deptno,variance(sal) from emp group by deptno;

4. 带有rollup和cube操作符的Group By

rollup 按分组的第一个列进行统计和最后的小计

cube 按分组的所有列的进行统计和最后的小计

select deptno,job ,sum(sal) from emp group by deptno,job;

select deptno,job ,sum(sal) from emp group by rollup(deptno,job);

cube 产生组内所有列的统计和最后的小计

select deptno,job ,sum(sal) from emp group by cube(deptno,job);