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  • PHP之路——MySql基础操作语句

    1,创建数据库,create datebase 数据库名,在这里kenan建立一个数据库名为myfirstdb

    create database myfirstdb; 

    2,查看所有的数据库

    show databases;

    3,选择数据库,只有先选择数据库,才能在选择的数据库中进行数据库操作

    use myfirstdb; 

    4,删除数据库

    drop database myfirstdb; 

    数据库的增删改查 

    这里要先使用 use来选择要操作的数据库

    1,建立数据库表

    use myfirstdb;  
    create table user(  
    id int auto_increment primary key,  
    username varchar(50) not null,  
    password varchar(50) not null,  
    createtime datetime,  
    )

    这里创建了一个名为user 的表,id为int型的,auto_increatement表明这个是自增字段,primary key表明这个是主键,username varchar(50)表明userame是可变的字符长,not null表明该字段不能够为空,createtime datetime 字段cratetime是日期时间类型的。

    2, 查看表结构

    mysql> desc user;  
    +------------+-------------+------+-----+---------+----------------+  
    | Field      | Type        | Null | Key | Default | Extra          |  
    +------------+-------------+------+-----+---------+----------------+  
    | id         | int(11)     | NO   | PRI | NULL    | auto_increment |  
    | username   | varchar(50) | NO   |     | NULL    |                |  
    | password   | varchar(50) | NO   |     | NULL    |                |  
    | createtime | datetime    | YES  |     | NULL    |                |  
    +------------+-------------+------+-----+---------+----------------+  
    4 rows in set (0.01 sec)  
     
    mysql> show columns from user;  
    +------------+-------------+------+-----+---------+----------------+  
    | Field      | Type        | Null | Key | Default | Extra          |  
    +------------+-------------+------+-----+---------+----------------+  
    | id         | int(11)     | NO   | PRI | NULL    | auto_increment |  
    | username   | varchar(50) | NO   |     | NULL    |                |  
    | password   | varchar(50) | NO   |     | NULL    |                |  
    | createtime | datetime    | YES  |     | NULL    |                |  
    +------------+-------------+------+-----+---------+----------------+  
    4 rows in set (0.01 sec) 
    在这里展示了两种查看表结构的方式
    

    3,修改表结构

    添加列

    mysql> alter table user add age int;  
    Query OK, 0 rows affected (0.25 sec)  
    Records: 0  Duplicates: 0  Warnings: 0 

    修改列

    mysql> alter table user modify username varchar(30);  
    Query OK, 0 rows affected (0.19 sec)  
    Records: 0  Duplicates: 0  Warnings: 0 
    注意关键词 modify

    修改后的表结构

    mysql> desc user;  
    +------------+-------------+------+-----+---------+----------------+  
    | Field      | Type        | Null | Key | Default | Extra          |  
    +------------+-------------+------+-----+---------+----------------+  
    | id         | int(11)     | NO   | PRI | NULL    | auto_increment |  
    | username   | varchar(30) | YES  |     | NULL    |                |  
    | password   | varchar(50) | NO   |     | NULL    |                |  
    | createtime | datetime    | YES  |     | NULL    |                |  
    | age        | int(11)     | YES  |     | NULL    |                |  
    +------------+-------------+------+-----+---------+----------------+  
    5 rows in set (0.01 sec) 
    

      

    4,删除表

    mysql> drop table user;  
    Query OK, 0 rows affected (0.03 sec) 

    5,插入数据

    mysql> insert into user values(null,'kenan','kenan',now());  
    Query OK, 1 row affected (0.13 sec) 
    这里使用了日期函数,表示当前时间和日期,字符串要用单引号引起来

    6,查询数据

    mysql> select * from user;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    +----+----------+----------+---------------------+  
    1 row in set (0.00 sec)  
     
    mysql> select username,password from user;  
    +----------+----------+  
    | username | password |  
    +----------+----------+  
    | kenan    | kenan    |  
    +----------+----------+  
    1 row in set (0.00 sec) 
    第一句表示查询所有的字段从user表里边,在这里*表示所有,第二句表示单独查询username和password字段

    6,带有where字句的条件查询

    mysql> select * from user where id > 1;  
    mysql> select * from user where username = 'kenan';  
    mysql> select * from user where username = 'kenan' and id = 1; 
    这里分别进行了三个带有where字句的子查询,分别对id,和username进行限制,用and 连接两个限制条件

    7,group by 对查询结果进行分组

    mysql> select * from user;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec)  
     
    mysql> select * from user group by username;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    +----+----------+----------+---------------------+  
    2 rows in set (0.04 sec)  
     
    mysql> select username,avg(id) from user group by username;  
    +----------+---------+  
    | username | avg(id) |  
    +----------+---------+  
    | kenan    |  2.0000 |  
    | lele     |  2.0000 |  
    +----------+---------+  
    2 rows in set (0.04 sec)  
    mysql> select username,sum(id) from user group by username;  
    +----------+---------+  
    | username | sum(id) |  
    +----------+---------+  
    | kenan    |       4 |  
    | lele     |       2 |  
    +----------+---------+  
    2 rows in set (0.03 sec) 
    这里展示的group by的用法,首先第一句是按照username分组,所以 username相同的数据会认为是一组
    只显示第一条数据,第二个sql语句和第三个sql语句用了两个分组函数avg(),sum()函数,这两个函数
    呢,是跟group by 配合使用的,avg()是用来求这一组数据的平均值,而sum()是用来求这一组数据的
    和。

    8,order by 对结果进行排序

    mysql> select * from user;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec)  
     
    mysql> select * from user order by username;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec)  
     
    mysql> select * from user order by id;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec)  
     
    mysql> select * from user order by id desc 
        -> ;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec)  
     
    mysql> select * from user order by username,id;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.00 sec) 
    在这里第一个sql语句,查出所有的user表中的数据,默认是按照你插入时的数据来排序,就是id递增
    第二句是 按照username排序,这个会比较username的首字母
    order by id 是按照id递增排序
    order by id desc 是按照id递减排序,这里大家明白 desc的作用了吧
    order by username,id是添加了两个排序条件,首先按照username排序,username相同的话,会按照id排序
    在排序中如果遇到NULL值,把NULL值按照最小的值来处理

    9,distinct的用法

    mysql> select distinct username from user;  
    +----------+  
    | username |  
    +----------+  
    | kenan    |  
    | lele     |  
    +----------+  
    2 rows in set (0.00 sec) 
    distinct的是去重,然后把不重复的查询出来

    10,like模糊查询

    mysql> select * from user where username like 'ke%';  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    2 rows in set (0.00 sec)  
     
    mysql> select * from user where username like '_e%';  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    3 rows in set (0.01 sec) 
    在这里用了like模糊查询
    第一个sql语句,是查询出来 uername 以 ke 开头的 行
    第二个sql语句,是查询出来 username 的第二个字母是e的行
    在这里%表示0或多个字符,_代表一个字符

    11,LIMIT 限定结果行数,用来进行分页查询

    mysql> select * from user limit 1;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  1 | kenan    | kenan    | 2012-10-30 21:46:31 |  
    +----+----------+----------+---------------------+  
    1 row in set (0.00 sec)  
     
    mysql> select * from user limit 1,2;  
    +----+----------+----------+---------------------+  
    | id | username | password | createtime          |  
    +----+----------+----------+---------------------+  
    |  2 | lele     | lele     | 2012-10-31 15:01:20 |  
    |  3 | kenan    | lele     | 2012-10-31 15:06:46 |  
    +----+----------+----------+---------------------+  
    2 rows in set (0.00 sec) 
    limit的两种用法
    第一种limit 1这个是显示查询出来的数据的第一条 当让1换成x,就是x条
    第二种limit 1,2这里limit带有的两个参数
                  首先我们把查询出来的数据进行编号,从0号开始(当然这个编号是不存在的,就是说表内不存在这个字段),它不是id
                  这个编号是便于我们理解人为的编号
                  然后第一个参数代表的含义呢,就是要显示的数据的编号
                  第二个参数表示的就是从刚刚编号开始(包含选中的编号)显示多少条数据
    分页用法,要显示第x页的数据,每页显示y条
    首先计算第x也的数据的开始编号是(x-1)*y
    所以这个sql语句应该这样写
    select * from user limit (x-1)*y,y;

    12,修改记录 

    mysql> update user set createtime = now() where username = 'kenan';  
    Query OK, 2 rows affected (0.05 sec)  
    Rows matched: 2  Changed: 2  Warnings: 0
    这里把user表中的所有username叫做kenan的记录更新createtime字段,更新为当前时间

    13,删除记录

    mysql> delete from user where username = 'lele';  
    Query OK, 1 row affected (0.06 sec) 
    这里删除user表中所有username叫做lele的记录

    原文链接:http://soukenan.blog.51cto.com/5130995/1045340
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  • 原文地址:https://www.cnblogs.com/xj76149095/p/5513420.html
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