昨天做了个BIGO的笔试，发现考的很多SQL语句我都有点模糊。想把这些常用的常考的sql语句做一下整理。还是那种感觉，更多东西你好像懵懵懂懂的知道，但是实际问到了让你手撕代码又很虚，还是要注重基础及整理啊。任重道远，加油！！
MySQL常用命令
create database name; 创建数据库
use database name; 选择数据库
drop database name 直接删除数据库，不提醒
show tables; 显示表
describe table name; 表的详细描述
select中加上distinct去除重复字段
说明：几个简单的基本的sql语句
选择：select * from table1 where 范围
插入：insert into table1(field1,field2) values(value1,value2)
删除：delete from table1 where 范围
更新：update table1 set field1=value1 where 范围
查找：select * from table1 where field1 like ’%value1%’ ---like的语法很精妙，查资料!
排序：select * from table1 order by field1,field2 desc
总数：select count as totalcount from table1
求和：select sum(field1) as sumvalue from table1
平均：select avg(field1) as avgvalue from table1
最大：select max(field1) as maxvalue from table1
最小：select min(field1) as minvalue from table1
增加一个列：Alter table tabname add column col type
添加主键： Alter table tabname add primary key(col）
创建索引：create [unique] index idxname on tabname(col….) 注：索引是不可更改的，想更改必须删除重新建。
#创建表create table student(
id int auto_increment primary key,
name varchar(50),
sex varchar(20),
date varchar(50),
content varchar(100)
)default charset=utf8;
#查看表的结构
describe student; #可以简写为desc student;
#插入数据
insert into student values(null,'aa','男','1988-10-2','......');
insert into student values(null,'bb','女','1889-03-6','......');
insert into student values(null,'cc','男','1889-08-8','......');
insert into student values(null,'dd','女','1889-12-8','......');
insert into student values(null,'ee','女','1889-09-6','......');
insert into student values(null,'ff','null','1889-09-6','......');
#查询表中的数据select * from student;select id,name from student;
#修改某一条数据update student set sex='男' where id=4;
#删除数据delete from student where id=5;
# and 且
select * from student where date>'1988-1-2' and date<'1988-12-1';
# or 或
select * from student where date<'1988-11-2' or date>'1988-12-1';
#between
select * from student where date between '1988-1-2' and '1988-12-1';
#in
查询制定集合内的数据select * from student where id in (1,3,5);
#排序 asc 升序 desc 降序
select * from student order by id asc;
#分组查询 #聚合函数
select max(id),name,sex from student group by sex;
select min(date) from student;
select avg(id) as '求平均' from student;
select count(*) from student; #统计表中总数
select count(sex) from student; #统计表中性别总数 若有一条数据中sex为空的话,就不予以统计~
select sum(id) from student;
#查询第i条以后到第j条的数据(不包括第i条)
select * from student limit 2,5; #显示3-5条数据
#巩固练习
create table c(
id int primary key auto_increment,
name varchar(10) not null,
sex varchar(50) , #DEFAULT '男' ,
age int unsigned, #不能为负值(如为负值 则默认为0)
sno int unique #不可重复
);