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1. Definitions
One-way function can be nested or nested, and the nesting function can only two packets.
2, Grammar
Packet format is the following three kinds of functions:
- G1(Group_item) = Result
如SUM(Group_item),AVG(Group_item) - G1(G2(Group_item)) = Result
如SUM(AVG(Group_item)) - G1 (G2 (G3 (Group_item) )) = Result
Note, this particular format is not allowed. The MAX (SUM (AVG (Group_item) )) Note that the function can not be applied to a single value of the packet, this would be written in a final value Max selecting the maximum value.
3, Code
/*
作者：AT阿宝哥
日期：2016年9月18日
愿景：参考官方资料，做最好的课程，成就更多职业人！
邮箱：[email protected]
CSDN：https://blog.csdn.net/goldentec
简书：https://www.jianshu.com/u/8a6075d7a2e0
说明：
注意：
*/
-------------------------------------------------------------------------------
--Sample1:
SELECT sum(comm) ,nvl(deptno,0)
FROM emp
WHERE nvl(deptno,0) IN (40,80,0)
Group by deptno;
SELECT avg( sum( comm ) )
from emp
where nvl(deptno,0) IN (40,80,0)
Group by deptno;
-------------------------------------------------------------------------------
--Sample2:错误,分组函数的嵌套太深.
select count(SUM(avg(sal))) from emp; --group function is nested too deeply
-------------------------------------------------------------------------------
--Sample3:在分组函数中可以嵌套单行函数.
select SUM( avg( length(ename) ) ) from emp group by deptno;
-------------------------------------------------------------------------------
