mysql 行增删改查

一、增

insert into student(name, age) values('tom', 20);
insert into student(name, age) values('tom', 18),('joker', 18);
insert into student(name, age) select name, age from info;

二、删

delete from db1;
delete from db1 where 条件判断
delete from db1 where 条件判断 and 条件判断
delete from db1 where 条件判断 or 条件判断
    条件判断
        =    !=
        <    <=
        >    >=
truncate table db1;

三、改

update db1 set name = 'master';
update db1 set name = 'joker' where age = 20;

四、查

前面
    select * from db1;
    select name,age from db1;
    select name as n, age from db1; 别名
    select name,1 from db1;
条件
    select * from tb1 where name = 'tom'；    # 条件判断
    select * from tb1 where name = 'tom' and age >1；
    select * from tb1 where name = 'tom' or name = 'joker';
    select * from tb1 where name in ('tom', 'joker')
    select * from tb1 where name not in ('tom', 'joker');
    select * from tb1 where id between 1 and 5; # 闭区间
    select * from tb1 where id in(select id from info);
通配符
    select * from tb1 where name like 'a%';
    select * from tb1 where name like 'a_';
    注意：% 匹配任意字符，_ 匹配一个字符
分页
    select * from tb1 limit 位置, 长度;    # 若limit后面，只有一个参数，则是长度
    select * from tb1 limit 长度 offset 位置;
排序
    select * from tb1 order by id asc;
    select * from tb1 order by id desc;
分组
    select count(cid), caption from class group by caption;
    select count(cid), caption from class where id > 5 group by caption having count(cid) >1;
    聚合函数： max(列) min(列) sum(列) avg(列) count(列) 计算
    注意：对聚合函数的结果进行比较要使用 having 相当于 where, where 在 最前面
连表操作
    select * from userinfo1,department where userinfo.id=department.d_id;
    # 不常用
    select * from userinfo
        left join department on userinfo.id=department.d_id;
    # 左边全显示,右边没有补NULL
    select * from userinfo
        inner join department on userinfo.id = department.d_id;
    # 不显示NULL
    select * from userinfo
        right join department on userinfo.id = department.d_id;
    # 右边的全显示,左边没有补NULL

    注意：left join, right join, inner join, 都用on ',' 用where
          前面的列，若是表有相同的列 表名.列名 来表示

补充

1.distinct 有去重的效果，但最好不要使用，效率低
　　select distinct username from userinfo;
2.查询多个表，会出现笛卡尔积现象  
3.映射可以是查询语句
　　select (select name from info) from userinfo; 
4.条件语句
　　case when 条件 then 为True else 为false end
6.判断是否为空
　　if(isnul(数据), 0, 1)
7.unoin
　　上下链表，注意列要一样
　　具有去重的作用，union all不去重
select * from userinfo
union
select * from info;