5,mysql数据库操作和SQL语言

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)

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

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)

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)

 

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;

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)

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)

9，distinct的用法

mysql> select distinct username from user;
+----------+
| username |
+----------+
| kenan    |
| lele     |
+----------+
2 rows in set (0.00 sec)

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)

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)

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

13，删除记录

mysql> delete from user where username = 'lele';
Query OK, 1 row affected (0.06 sec)

今天就写到这里吧，这个是最长的一片博客了，大家有问题可以回复我哦！