Mysql 查询,删除
//查看表的内容
select * from hpeu_student;
//从第一行查找五行
select * from hpeu_student limit 5;
//从第一行的下零行查找5行
select * from hpeu_student limit 5 offset 0;
//从第一行的下一行查找5行
select * from hpeu_student limit 5 offset 1;
select * from hpeu_student limit 1,5;
//where 后面指定条件 stu_id<4 and stu_name='jim';where通常把小表放在前面,范围小提高效率
select * from hpeu_student where stu_id = 4;
//like的用法:stu_id 含有5的 而且 stu_name含有uc的
select * from hpeu_student where stu_id like '%5%' and stu_name like '%o%';
//order by 排序(desc降序 asc升序) stu_id含有1的按照 stu_name升序排序
select * from hpeu_student where stu_id like '%1%' order by stu_name asc;
//group by 分组 两次筛选后面加 order by 字段 单个必须把name作为主要字段,加入order by可以加多个字段
select * from hpeu_student where stu_id <5 group by stu_name;
select stu_id,stu_name from hpeu_student where stu_id <5 group by stu_name;//报错count(str_id)就不会报错 count(str_id) as id 起别名id
//having(分组条件) 针对order by 分组之后的再筛选条件,行过滤
select * from hpeu_student where stu_id <5 group by stu_id having stu_id=3;
//更新数据 set 后面可以有多个更改,where是条件,没有就会全部更改
update table set stu_name='Mike' where stu_id=1;
//删除数据库(真正的环境中通常都不使用drop)
drop database Test
//删除表,删除表结构,必须要从新 新建表
drop table hpeu_student;
//删除表的全部内容,不删除表结构,不能与where一起使用,删除索引,stu_id会从1开始
truncate hpeu_student;
//delete 删除可以where 加条件删除,不会删除索引,stu_id会从后面开始
delete hpeu_student where stu_id>4;