SQL基础语句总结

#显示数据库
show databases;

#判断是否存在数据库test_mysql,有的话先删除
drop database if exists test_mysql;

#创建数据库
create database test_mysql;

#删除数据库
drop database test_mysql;

#使用该数据库
use test_mysql;

#显示数据库中的表
show tables;

#先判断表是否存在,存在先删除
drop table if exists student;

#创建表
create table student(
id int auto_increment primary key,
name varchar(50),
sex varchar(20),
date varchar(50),
)default charset=utf8;

#删除表
drop table student;

#查看表的结构
describe student;  #可以简写为desc student;

#插入数据
insert into student values(null,'test','2018-10-2');

#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 name='jack' where id=4;

#删除数据
delete from student where id=8;

# and 且
select * from student where date>'2018-1-2' and date<'2018-12-1';

# or 或
select * from student where date<'2018-11-2' or date>'2018-12-1';

#between
select * from student where date between '2018-1-2' and '2018-12-1';

#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 'Avg' 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

#修改数据
update student set name='test' where id=2;
update student set name='花花',sex='女' where id=2
delete from student where id=2;

#修改表的名字
#格式:alter table tbl_name rename to new_name
alter table student rename to test_1;

#向表中增加一个字段(列)
#格式:alter table tablename add columnname type;/alter table tablename add(columnname type);
alter table student add  age varchar(20) set default '1'; #set default 设置默认值

#修改表中某个字段的名字
alter table tablename change columnname newcolumnname type;  #修改一个表的字段名
alter table student change name test_name varchar(50);

#去掉表中字段age的默认值
alter table student alter age drop default;

#去掉表中字段age
alter table student drop column age;

#删除表中主键
alter table student drop primary key;

#表中增加主键
#alter table add primary key (column1,column2,....,column)
alter table student add primary key (student_id);

#用文本方式将数据装入数据库表中（例如D:/mysql.txt）
load data local infile "D:/mysql.txt" into table MYTABLE;

#导入.sql文件命令（例如D:/mysql.sql）
source d:/mysql.sql;  #或者  /. d:/mysql.sql;