2020.03.13 DML语言

-- select sum( province_id) as '全国的大学' from student.school;
-- select count(province_name) from student.school;
-- select sum(province_id + ifnull(province_id,0)) from student.school;
-- select max(school_id) from student.school;
-- select count(*),sum( province_id), format(avg(school_id),2),max(school_id) from student.school;
-- select province_name,city_id from student.school group by city_id;
-- 关联查询，记得添加关联条件!
-- select short_name,city_name from student.edu_school,student.school where edu_school.school_no=school.school_id;
-- select DISTINCT(province_name) from student.school;