mysql
一 查询:
students学生表,grade 成绩表
1.查询全部数据
select * from students
2.查询表的别名
select s.name,s.age from students s
3.多表查询
select s.name,s.age g.score,g.kemu from students s join grade g on s.id=g.id
4.内连接 (查询students表和grade表的交集)
select * from students inner join grade on students.id=grade.id
5.外连接(left join 和 right join )
select * from students left join grade on students.id=grade.id (查询students表的全部+grade表匹配的值)
select * from students right join grade on students.id=grade.id (查询grade表的全部students表匹配的值)
6.删除数据
delete from students where id=11001
7.修改数据
update students set age=20 where id=11001
8.新增数据
INSERT INTO `mysql`.`students` (`id`, `name`, `age`) VALUES ('11004', '王二', '20');
9.排序
select * from grade order by score asc 升序
select * from grade order by score desc 降序
10 分组
select class,sum(amount) as m from origin GROUP BY class
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