MySQL基础语法详解-优快云博客

本文介绍了MySQL的基本语法，包括数据查询、插入、更新和删除等操作，适用于初学者掌握数据库操作。

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MySQL-基础语法

#启动mysql服务器
net start mysql
 
#关闭 
net stop mysql
  
#进入
mysql -h 主机地址 -u 用户名 －p 用户密码
 
#退出
exit

status;
显示当前mysql的version的各种信息。
 
#-----MySql数据库操作基础-----
 
#显示数据库
show databases;
 
#判断是否存在数据库wpj1105,有的话先删除
drop database if exists xianyu007;
 
#创建数据库
create database xianyu007;
 
#删除数据库
drop database xianyu007;
 
#使用该数据库
use xianyu007;
 
#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),
content varchar(100)
)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,'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 count(ifnull(sex,0)) from students #统计表中性别总数  若有一条数据中sex为空也统计~
 
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 c set age=66 where id=2;
update c set name='花花',age=21,sex='女' where id=2
delete from c where age=21;
 
#常用查询语句
select name,age ,id from c
select * from c where age>40 and age<60;  #and
select * from c where age<40 or age<60;  #or
select * from c where age between 40 and 60 #between
select * from c where age in (30,48,68,99);     #in 查询指定集合内的数据
select * from c order by age desc;      #order by （asc升序 des降序）
 
#分组查询
select name,max(age) from c group by sex;  #按性别分组查年龄最大值

#聚合函数
select min(age) from c;
select avg(age) as '平均年龄 ' from c;
select count(*) from c;  #统计表中数据总数
select sum(age) from c;
 
#修改表的名字
#格式:alter table tbl_name rename to new_name
alter table c rename to a;
  
#表结构修改
create table test
(
id int not null auto_increment primary key, #设定主键
name varchar(20) not null default 'NoName', #设定默认值
department_id int not null,
position_id int not null,
unique (department_id,position_id) #设定唯一值
);
 
#修改表的名字
#格式:alter table tbl_name rename to new_name
alter table test rename to test_rename;
 
#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 test add  columnname varchar(20);
 
#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 test change name uname varchar(50);
 
select * from test;
 
#表position 增加列test
alter table position add(test char(10));

#表position 修改列test
alter table position modify test char(20) not null;

#表position 修改列test 默认值
alter table position alter test set default 'system';

#表position 去掉test 默认值
alter table position alter test drop default;

#表position 去掉列test
alter table position drop column test;

#表depart_pos 删除主键
alter table depart_pos drop primary key;

#表depart_pos 增加主键
alter table depart_pos add primary key PK_depart_pos
(department_id,position_id);

# 表students 增加外键
alter table students add foreign key(cls_id) references classes(id);

# 表students 查看外键
alter table teacher drop foreign key 外键名;

# 表students 删除外键
alter table teacher drop foreign key 外键名;


# 内连接查询语法格式:
# select 字段 from 表1 inner join 表2 on 表1.字段1 = 表2.字段2
select * from students as s inner join classes as c on s.cls_id = c.id;
 
# 左连接查询语法格式:
# select 字段 from 表1 left join 表2 on 表1.字段1 = 表2.字段2
select * from students as s left join classes as c on s.cls_id = c.id;

# 右连接查询语法格式:
# select 字段 from 表1 right join 表2 on 表1.字段1 = 表2.字段2
select * from students as s right join classes as c on s.cls_id = c.id;

# 自连接查询
# 自连接查询必须对表起别名
# 自连接查询就是把一张表模拟成左右两张表，然后进行连表查询。
# 自连接就是一种特殊的连接方式，连接的表还是本身这张表
select c.id, c.title, c.pid, p.title from areas as c inner join areas as p on c.pid = p.id where p.title = '山西省';

#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;