Queries using aggregate functions

COUNT () function

1, COUNT () function is used to count the number of records;

SELECT COUNT(*) FROM t_grade;

SELECT COUNT(*) AS total FROM t_grade;

2, used in conjunction with GOUPE BY keyword;

SELECT stuName,COUNT(*) FROM t_grade GROUP BY stuName;

SUN () function

1, SUM () function is a summation function;

SELECT stuName,SUM(score) FROM t_grade WHERE stuName="张三";

2, used in conjunction with GOUPE BY keyword;

SELECT stuName,SUM(score) FROM t_grade GROUP BY stuName;

AVG () function

1, AVG () function is a function of averaging;

SELECT stuName,AVG(score) FROM t_grade WHERE stuName="张三";

2, used in conjunction with GOUPE BY keyword;

SELECT stuName,AVG(score) FROM t_grade GROUP BY stuName;

MAX () function

1, MAX () function is a function of the maximum demand;

SELECT stuName,course,MAX(score) FROM t_grade WHERE stuName="张三";

2, used in conjunction with GOUPE BY keyword;

SELECT stuName,MAX(score) FROM t_grade GROUP BY stuName;

MIN () function
1, MIN () function is a function of selecting the minimum value;

SELECT stuName,course,MIN(score) FROM t_grade WHERE stuName="张三";

2, used in conjunction with GOUPE BY keyword

SELECT stuName,MIN(score) FROM t_grade GROUP BY stuName;