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