MySQL函数

1.常用函数
1
2
3
--需要的时候就去官方文档寻找
SELECT USER();
SELECT VERSION();
2.聚合函数
1
2
3
4
5
6
7
8
9
10
11
12
13
--数量求和
SELECT count(*) as '数量总和'FROM `subject`--求的是行数
SELECT count(1) as '数量总和'FROM `subject`
SELECT count(`subject`.subjectno) as '数量总和'FROM `subject`
--聚合函数求最大最小，求和，求均值
SELECT AVG(result.studentresult) as '平均值' FROM result
SELECT sum(result.studentresult) as '总和' FROM result
SELECT max(result.studentresult) as '最大值' FROM result
SELECT min(result.studentresult) as '最小值' FROM result
--结合
SELECT AVG(result.studentresult) as '平均值' FROM result 
GROUP BY result.studentresult
HAVING 平均值>70;