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MySQL_Aggregate_Functions

2016-05-04 00:00 309 查看

摘要: Count -- Sum -- Avg -- Max -- Min

1. Count

select count(*) from t_grade;
select count(*) as total from t_grade;
select count(*) from t_grade group by stuName;
select stuName, count(*) from t_grade group by stuName;

2. Sum

select stuName, sum(score) from t_grade where stuName='张三';
select stuName, sum(score) as totalScore from t_grade where stuName='张三';
select stuName, sum(score) as totalScore from t_grade group by stuName;

3. Avg

select stuName, avg(score) as averageScore from t_grade where stuName='张三';
select stuName, avg(score) as averageScore from t_grade group by stuName;

4. Max

select stuName, max(score) as maxScore from t_grade where stuName='张三';
select stuName, max(score) as maxScore from t_grade group by stuName;
select stuName, course, max(score) as maxScore from t_grade where stuName='张三';
select stuName, course, max(score) as maxScore from t_grade group by stuName; /* False, because 'group by stuName', */
/* so it has to set only 'stuName' after 'select' */

5. Min

select stuName, course, min(score) as maxScore from t_grade where stuName='张三';
select stuName, min(score) as maxScore from t_grade group by stuName;

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