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1. Definitions
SUM function returns a non-null set of digital sum value of the expression
2, Grammar
The syntax is as follows:
SUM( [DISTINCT | ALL] expr )
This syntax can be decomposed as follows:
- SUM (DISTINCT expr)
provides a unique value expr After calculating each row in the group will be returned and obtained by adding. - SUM (ALL expr)
providing group, and the sum of each row and expr and ignores null values. - SUM(expr)
Note :
Data expr type argument must be NUMBER.
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(2) FROM emp;
select sum(3) from emp;
SELECT sum(4) FROM emp;
-------------------------------------------------------------------------------
--Sample2:获得组(整个表)中各行SAL列值并相加,忽略空值.
SELECT * FROM emp;
SELECT sum(sal) FROM emp;
SELECT sum(comm) FROM emp;
-------------------------------------------------------------------------------
--Sample3:将列中的唯一值添加到总和之中.
SELECT * FROM emp;
SELECT sum(DISTINCT sal) FROM emp;
SELECT sum(DISTINCT comm) FROM emp;
-------------------------------------------------------------------------------
