MySQL笔记之函数查询的使用

参考表

count()用来统计记录的条数

mysql> select count(*) from score;
mysql> select count(*) from score where stu_id=901;

sum()求和函数

mysql> select sum(grade) from score;
mysql> select id,sum(grade) from score where stu_id=901;

avg()求平均值函数

mysql> select avg(grade) from score where c_name='计算机';
mysql> select c_name,avg(grade) from score group by c_name;

max()求最大值函数

mysql> select c_name,max(grade) from score where c_name='英语';
mysql> select c_name,max(grade) from score group by c_name;

min()求最小值函数

mysql> select c_name,min(grade) from score where c_name='中文';
mysql> select c_name,min(grade) from score group by c_name;

concat拼接函数

mysql> select concat(c_name, '(', stu_id, ')')
    -> from score order by stu_id;