SQL的使用

时间：2017-09-01 00:09:57 阅读：248 评论：0 收藏：0 [点我收藏+]

标签：一个 socket insert word mysql 多表查询正则表达本地数值

一、数据库增删改查

基本操作

1.创建数据库

create database zhuziqin;

2.删除数据库

drop database zhuziqin;

3.创建一个用户表

mysql> use db1;
mysql> create table user(id int,name varchar(30),pass varchar(30));
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| user          |
+---------------+
mysql> select * from user;
Empty set (0.00 sec

4.插入数据

mysql> insert into user(id,name,pass) values("1","zhangsan","123");
Query OK, 1 row affected (0.01 sec)

mysql> select * from user;
+------+----------+------+
| id   | name     | pass |
+------+----------+------+
|    1 | zhangsan | 123  |
+------+----------+------+
1 row in set (0.00 sec)

5.删除一个表

drop table user;

6.查看表字段

desc table user;

7.查看表数据

mysql> select * from user;
+------+----------+------+
| id   | name     | pass |
+------+----------+------+
|    1 | zhangsan | 123  |
+------+----------+------+

8.修改表名

mysql> rename table user to hehe;

9.更新数据

mysql> update hehe set pass="newpass" where pass=123; #把密码更新为newpass

mysql> update hehe set id=10,name="lisi" where id =1; #把id记录的name更新为id10和name为lisi

10.重命名字段名

mysql> alter table hehe change pass newname varchar(30);

11.表中添加一个字段

mysql> alter table hehe add age int;
Query OK, 0 rows affected (0.18 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from hehe;
+------+------+---------+------+
| id   | name | newname | age  |
+------+------+---------+------+
|   10 | lisi | newpass | NULL |
+------+------+---------+------+

12.修改字段

alter table user modify age int no null default 20; #当年龄输入为空时，默认为20岁

13.删除表中的一个字段

alter table user drop age;

14.删除一条记录

delete from user where id=1;

15.查找一条记录

select id,name,pass from user where id=1;

16.删除ID记录

delete from user where id>=3 id<=5; #删除大于3小于5的id

delete from user where id in(1,3,5); #删除1,3,5的id

delete from user where id=1 or id=3 or id=5; #删除1,3,5的id

delete from user where id between 1 and 5; #删除1至5的id

高级查询

1.返回结果删除重复项

select distinct id from user;

2.查询字段中为NULL

select * from where pass is null;

select * from where pass is not null; #查询不为NULL的

3.like模糊查询,包含zhang的列出来

select * from user where name like ‘%zhang%‘;

select * from user where name like ‘%zhang%‘ or name like ‘%li%‘;#查找包含zhang或li的列出来

也可以使用正则表达式查询,生产环境一般不用的，因为查询慢，效果一样

select * from user where name regexp ‘li‘;
4.使用order by对查询结果排序(升序/降序)，默认是升序

select id,name,pass from user order by id asc/desc;

5.使用limit取出排名前三个

select * from user order by id desc limit 3;

6.concat函数使用-字符串连接符

mysql> select id,name,pass,concat(id,‘_‘,name) idname from user;

+----+----------+------+------------+

+----+----------+------+------------+

| 1 | zhangsan | 123 | 1_zhangsan |

| 2 | lisi | 123 | 2_lisi |

| 3 | zhaowu | 123 | 3_zhaowu |

+----+----------+------+------------+

7.rand函数随机排序，如随机抽取前三名

select * from user order by rand() limit 3;

8.count统计,如统计多少个id记录

select count(*) count from user;

#count为自定义显示查询结果后字段名，*为mysql优化后的查询方法，要比直接写入id效率高

select count(id) from user where name=‘zhangsan‘; #统计zhangsan多少条记录

9.sum求和，如统计同消费了多少钱

select sum(id) from user where name=‘lisi‘; #所有id数加在一起

10.avg平均数,如求班级平均分

select avg(id) from user;

11.max最大值，如得到一个最高分

select max(id) from user;

12.min最小值

select min(id) from user;

13.group by分组聚合

select name,count(id) from user group by name order by desc;

#使用count来聚合，基于name分组，再order by排序下（一般排名都使用分组聚合）

select name,count(id) count from user group by name having count>=3;

#查询前三名，having是对分组的结果进行筛选，这不能用where，count代表查询结果后显示的字段名

14.普通多表查询（前提：两个表必须有关系）

先创建两个有关系的表：

create table user(id int unsigned auto_increment primary key,name varchar(30),age int);

create table post(id int unsigned auto_increment primary key,uid int,title varchar(200),content text);

结果一：查询用户发的所有记录

select user.name,post.title,post.content from user,post where user.id=post.uid;

结果二：统计每个用户有多少个记录

select user.name,post.title,post.content count(id) from user,post where user.id=post.uid group by user.name;

15.联表查询（查询成绩）

mysql> select * from tb1;

+------+----------+

| id | name |

+------+----------+

| 1 | zhangsan |

| 2 | lisi |

+------+----------+

mysql> select * from tb2;

+------+-------+

| id | score |

+------+-------+

| 1 | 80 |

| 2 | 81 |

+------+-------+

mysql> select tb1.name,tb2.score from tb1,tb2 where tb1.id = tb2.id;

+----------+-------+

| name | score |

+----------+-------+

| zhangsan | 80 |

| lisi | 81 |

+----------+-------+

二、表字段类型

1.数值

int(size)：整型，只能存整数数字，不能为空，默认允许输入null，也可以设置不允许写（not null）

float：浮点型，可以写入整数或浮点数

1.1字段属性

unsigned：无符号，全是整数

zerofill：与长度无关，不够3位时前面补0，默认看不见

null与not null：允许输入null和不允许输入

default：不允许null情况下，当输入空时，则使用默认值

auto_increment：一般自增ID

1.2示例

例如，设置id为自增：

create table user(id int unsigned auto_increment primary key,name varchar(30),pass varchar(30));

primary key：有auto_increment必须设置为主键索引，提供查询速度，再插入就不用写id列了，如果你写了，就以你写的为准，继续自增。

例如，创建一个表，当输入性别为空时，默认则为男：

create table user2(id int unsigned auto_increment primary key,name varchar(30),sex varchar(5) not null default "nan");

查看字段信息：

mysql> desc user2;

+-------+------------------+------+-----+---------+----------------+

+-------+------------------+------+-----+---------+----------------+

| id | int(10) unsigned | NO | PRI | NULL | auto_increment |

| sex | varchar(5) | NO | | nan | |

+-------+------------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

2.字符串

char(size）：占用size的字节，但查询速度快，最大支持255个字符

varchar(size)：存多少占多少，剩点空间，最大支持65535个字符

text：支持65535字节

longtext：支持42亿字节

3.日期类型（有的会使用int类型来存时间戳）

以下是官方说法占用的字节，但实际会有不符。

date：年月日，占用3个字节

time：时分秒，占用3个字节

datetime：年月日时分秒，占用8个字节

year：年，占用1个字节

三、用户管理

1.设置Mysql密码

方法一：set password=password（‘newpass‘）;

方法二：update user set password=password（‘newpass‘） where user=‘root‘;

方法三：grant all on *.* to ‘root‘@‘localhost‘ identified by ‘newpass‘;

再刷新：flush privileges;

2.创建用户并授权

grant all privileges on *.* to ‘user‘@‘localhost‘ identified by ‘pass‘;

*.*：对应的是数据库/表的权限

localhost：只允许本地访问，也可以设置%为所有访问

3.撤销用户权限

revoke all privileges on *.* from ‘root‘@‘localhost‘ identified by ‘pass‘;

四、数据库字符集

1.查看服务器基本信息\s

mysql> \s

--------------

mysql Ver 14.14 Distrib 5.5.34, for Linux (x86_64) using EditLine wrapper

Connection id: 141700

Current database: lab

Current user: root@localhost

SSL: Not in use

Current pager: stdout

Using outfile: ‘‘

Using delimiter: ;

Server version: 5.5.34-log Source distribution

Protocol version: 10

Connection: Localhost via UNIX socket

Server characterset: latin1

Db characterset: latin1

Client characterset: latin1

Conn. characterset: latin1

UNIX socket: /tmp/mysql.sock

Uptime: 47 days 4 hours 54 min 1 sec

Threads: 4 Questions: 189434783 Slow queries: 1 Opens: 283512 Flush tables: 23 Open tables: 46 Queries per second avg: 46.447

--------------

可以看到四种默认字符集是latin1，修改四种默认字符集，client和connection两个要是一样的。

set character_set_server=utf8;

set character_set_database=utf8;

set character_set_client=utf8;

set character_set_connection=utf8;

也可以修改my.cnf默认字符集

[mysqld]

character_set_server=utf8

[mysql]

default-character-set=utf8

重启mysql！

2.查看创建数据库时使用的字符集

show create database mydb;

五、创建表字段索引

1.主键索引

1.1创建一个主键索引，一般创建表时已经设置

alter table user add primary key(id);

1.2删除一个主键索引

alter table user drop primary key;

2.普通索引

2.1创建一个普通索引

alter table user add index index_name(name);

2.2删除一个普通索引

alter table user drop index index_name;

2.3查看主键索引和普通索引

show index from user;

show keys from user;

注：修改字段名不影响索引。

3.查看表中创建的索引

mysql> desc user2;

+-------+------------------+------+-----+---------+----------------+

+-------+------------------+------+-----+---------+----------------+

| id | int(10) unsigned | NO | PRI | NULL | auto_increment |

+-------+------------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

上面key中的PRI代表是主键索引，MUL代表是普通索引。

4.查看索引信息

mysql> show index from user2;

+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

| user2 | 0 | PRIMARY | 1 | id | A | 1 | NULL | NULL | | BTREE | | |

| user2 | 1 | index_name | 1 | name | A | 1 | NULL | NULL | YES | BTREE | | |

+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

2 rows in set (0.00 sec)

可以看到user表，做了PRIMARY主键索引和index_name名字的普通索引。

5.测试是否使用索引

mysql> desc select id,name from user2 where name=‘zhangsan‘;

+----+-------------+-------+------+---------------+------------+---------+-------+------+--------------------------+

+----+-------------+-------+------+---------------+------------+---------+-------+------+--------------------------+

+----+-------------+-------+------+---------------+------------+---------+-------+------+--------------------------+

1 row in set (0.00 sec)

用desc检测语句，可以看到查询一条张三的记录，使用了普通索引index_name这个名字，检索了一行(rows)就找到了这条记录。

SQL的使用

标签：一个 socket insert word mysql 多表查询正则表达本地数值

原文地址：http://www.cnblogs.com/Achin/p/7448429.html