Mysql的增删改查语句

删除sex：alter table employee drop cpolumn sex;

修改name字段：alter table employee change column name username varchar(10);

改变usename字段长度：alter table employee change username username varchar(60);

改变usename字段类型：alter table employee change username username var(6);

添加主键约束：alter table employee add constraint pk_id primary key(id);

修改表名：rename table employee to user;

表的字符集：alter table user character set utf8;

添加索引：alter table user add index intind(id);

查询：select * from tstudent;

查多字段：select sid,name from tsdudent;

查字段改为中文：select sid as "学号", name as "姓名" from tstudent;

查询满足条件：select *from tcourse where chours=100;

select *from tcourse where chours<100;

选择查询：select *from tcourse where chours between 50 and 100;

select *from tcourse where (chours>=50) and (chours<=100);

select *from tcourse where chours in(100,72);

select *from tcourse where (chours=100) or (chours=72);

匹配查询：select *from tcourse where cname like"%m%";

排序默认asc升序：select *from tcourse order by chours;

desc降序： select *from tcourse order by chours desc;

统计记录:select count(*) from tcourse;

统计大于90:select count(*) from tcourse where chours>90;

课程总数:select sum(chours) from tcourse where cterm;

中文名:select sum(chours) as "学时",sum(credit) as "学分" from tcourse where cterm=1;

平均值AVG:select avg（chours) from tcours where cterm=1;

max与min:select max(chours),min(chours) from tcourse;

select addtime("02:30:20","01:00:01");

当前日期：select current_date();

select current_time

时间戳:select current_timestamp();

日期：select date("2010-01-01 16:00:01");

加时间：select birthday,date_add(birthday,interval 2 year) from tstudent;

select birthday,date_add(birthday,interval 2 day) from tstudent;

select birthday,date_add(birthday,interval 2 month) from tstudent;

select birthday,date_add(birthday,interval 2 week) from tstudent;

减时间：select birthday,date_sub(birthday,interval 2 year) from tstudent;

select birthday,date_sub(birthday,interval 2 day) from tstudent;

时间差:select datediff("1990-02-01","1990-01-01");

返回当前:select now(); select year/month/date(now());

字符串函数-->字符集:select charset("hello world");

select charset(name) from tstudent;

字符连接:select concat("hello","world");

转换大写:select ucase("hello");

转换小写:select lcase("WORLD");

字符长度:select length("hello");

在字符的位置:select instr("helloworld","wo");

左取字符:select left("hello world",5);

替换:select replace("hello world","lo","dd");

比较字符:select strcmp("aca","abb");

取字符:select substring("hello world",5,6);//从str的position开始,取length个字符

去空格:select rtrim(" hello world ");//右端

select ltrim(" hello world");//左端

select trim(" hello world ");//前后

select concat(trim("hello world"),"dd");

select concat("dd",trim("hello world"));

数学函数:

绝对值:select abs(-2);

转换进制:select conv(11,8,10);

向下取整:select floor(16.8);

保留小数倍数

:select format(16.2438,2);

随机数:select rand();

分组求和:select cterm,sum(chours) from tcourse group by cterm;

select cterm,sum(chours)from tcourse group by chours having sum(chours)>120;