MySQL的奇巧淫技

编程小蝉 06-30 2383

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mysql中的基本逻辑对象

mysql有这么几种对象

mysqld--->库---->表---->记录(由行和列组成)一条记录中的一列叫做字段

什么是关系型数据库

表与表发生关系，叫关系型

部门表（部门ID、部门名称）

雇员表（员工ID、员工姓名、部门ID）

可以通过上面的例子知道在雇员表中写入了部门id这个字段在部门表中也存在，2个表就通过部门id这个字段联系起来了

操作数据库的4种方式(使用SQL语句):

action:

查询数据(最多的动作) 就是查询数据

修改数据

删除数据

增加数据

常见的SQL标准

mysql=国际标准化＋mysql官方的自定义标准

pl/sql=国际标准化＋oracle官方的自定义标准

Tsql=国际标准化＋microsoft官方的自定义标准

总结:

所有大家在学习一些SQL语句的时候会出现我虽然没有学过这个数据库，但是它的语法我基本也能看的懂，就是因为SQL有国际标准化的语句

常用的SQL语句

create语句

创建数据库

mysql> create database ceshi1; #创建数据库ceshi1Query OK, 1 row affected (0.00 sec)mysql> show create database ceshi1; 查看数据库是如何建立的+----------+-------------------------------------------------------------------+| Database | Create Database |+----------+-------------------------------------------------------------------+| ceshi1 | CREATE DATABASE `ceshi1` /*!40100 DEFAULT CHARACTER SET latin1 */ |+----------+-------------------------------------------------------------------+1 row in set (0.00 sec)mysql> create database ceshi2 default charset utf8; 设置默认的字符编码集为utf-8Query OK, 1 row affected (0.00 sec)mysql> create database IF NOT EXISTS ceshi1 default charset utf8; #创建一个数据库如果不存在就创建，如果存在就告警Query OK, 1 row affected, 1 warning (0.00 sec)mysql> show warnings; #查看最后一次的waring的信息+-------+------+-------------------------------------------------+| Level | Code | Message |+-------+------+-------------------------------------------------+| Note | 1007 | Can't create database 'ceshi1'; database exists |+-------+------+-------------------------------------------------+1 row in set (0.00 sec)

创建表二维表(表由行和列组成，表必须存在于某一个库当中)

2个变量

varchar ----不定长比如我设一个字段为50个字符那么我只占用了30个字符那么数据库给我计算的时候只给我算30个字符

char ---定长比如我设置一个字段为50个字符，我只占用了10个字符，但是数据库还是会给我算50个字符的空间的占用

mysql> use ceshi1; #进入ceshi1库Database changedmysql> create table ceshi1.t1(id int,name varchar(50),salary decimal(10,2),dept varchar(50));Query OK, 0 rows affected (0.02 sec)解析: 在ceshi1库中创建t1表 并创建4个字段1. 第一个字段 id 设置int类型2. 第二个字段 name 指定字符长度为503. 第三个字段 salary 指定保留小数点2位4. 第四个字段 dept 执行字符长度为50mysql> DESCRIBE t1; #查看表结构 可以看到有4个字段+--------+---------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+--------+---------------+------+-----+---------+-------+| id | int(11) | YES | | NULL | || name | varchar(50) | YES | | NULL | || salary | decimal(10,2) | YES | | NULL | || dept | varchar(50) | YES | | NULL | |+--------+---------------+------+-----+---------+-------+4 rows in set (0.00 sec)mysql> select * from ceshi1.t1; 查询表所有内容Empty set (0.00 sec)mysql> insert into db01.t1 set id=1, name='zhang3',salary=5000,dept='生产部'; 插入数据Query OK, 1 row affected, 1 warning (0.07 sec)mysql> select * from ceshi1.t1; #可以看到数据已经插入进去了+------+--------+---------+-----------+| id | name | salary | dept |+------+--------+---------+-----------+| 1 | zhang3 | 5000.00 | 生产部 |+------+--------+---------+-----------+1 row in set (0.00 sec)mysql> show create table ceshi1.t1; #可以查看表示任何创建的| Table | Create Table | t1 | CREATE TABLE `t1` ( `id` int(11) DEFAULT NULL, `name` varchar(50) DEFAULT NULL, `salary` decimal(10,2) DEFAULT NULL, `dept` varchar(50) DEFAULT NULL) ENGINE=MyISAM DEFAULT CHARSET=latin1 可以查出使用神没存储引擎以及语言编码1 row in set (0.00 sec)mysql> create table ceshi1.t2 ( 列数多的情况可以使用一下方式创建表 -> `id` int(11) DEFAULT NULL, -> `name` varchar(50) DEFAULT NULL, -> `salary` decimal(10,2) DEFAULT NULL, -> `dept` varchar(50) DEFAULT NULL -> );Query OK, 0 rows affected (0.11 sec)

创建用户

创建一个用户 user01用户名 123密码mysql> create user user01@'localhost' identified by '123';Query OK, 0 rows affected (0.00 sec)mysql> set password for user01@'localhost'=password('123'); --设置用户的密码mysql> create user u01@'localhost' ; --创建一个用户mysql> select user,host,password from mysql.user; －－查询用户是否创建成功| root | localhost | *425F1EBD8227A2B1E01C475B523E27A592CFF59A || root | vagrant-centos65.vagrantup.com | || root | 127.0.0.1 | || | localhost | || | vagrant-centos65.vagrantup.com | || user01 | localhost | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257mysql> show grants; #查看用户权限| Grants for root@localhost || GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*425F1EBD8227A2B1E01C475B523E27A592CFF59A' WITH GRANT OPTION |1 row in set (0.00 sec)

drop --删除数据库对象(表/库/用户)

删除表/库 mysql> use ceshi1mysql> show tables;mysql> drop table t1; --删除表mysql> drop table t2; mysql> use ceshi1 --验证表是否删除成功mysql> show tablesmysql> drop database ceshi1; --删除库Query OK, 0 rows affected (0.00 sec)mysql> drop database ceshi1 ;mysql> show databases; --验证库是否删除成功

删除用户:

mysql> drop user user01@'localhost'; --删除用户Query OK, 0 rows affected (0.00 sec)mysql> select user from mysql.user where user='user01'; --验证用户是否删除成功mysql> drop user ''@'192.168.1.1'; 删除一个匿名用户

alter（修改已经存在数据库对象（库/表/列）的属性）

mysql> ALTER DATABASE db01 DEFAULT CHARACTER SET latin1; －－修改数据库语言编码Query OK, 1 row affected (0.05 sec)mysql> show create database db01; －－验证修改是否成功

修改表的属性：mysql> create table t2(name varchar(50));mysql> ALTER TABLE t2 ADD id int FIRST; --增加一列成为第一列mysql> ALTER TABLE t2 add id2 int AFTER id; --在id后面增加一列叫id2mysql> alter table t2 drop id2; --删除id2这个列mysql> alter table t2 change id ID bigint; --修改列名和数据类型mysql> alter table t2 modify ID int; --修改列的数据类型mysql> alter table t2 rename t20; --重命名表mysql>show engines; --查看数据库有哪些存储引擎mysql> alter table t20 engine MyISAM; --修改表的存储引擎mysql> show create table t20; --查看修改存储引擎是否成功mysql> alter table t20 DEFAULT CHARSET=utf8; －－修改表的语言编码

insert 插入记录

mysql> insert into ceshi1.t1 set id=1,name='zhang3'; --向指定列插入数据mysql> insert into ceshi1.t1 values(2,'li4'),(3,'wang5'),(4,'zhao6'); --插入多条记录mysql> insert into ceshi1.t1(NAME) values('test01'),('test02'),('test03'); --不写列名，表示按顺序往所有的列插入数据mysql> select * from ceshi1.t1 where id<5; 查出前4张表mysql> insert into ceshi1.t2 select * from ceshi1.t1 where id<5; 查出前4张表，插入到当前表（注意表结构要一致）mysql> rename tables t1 to t01;

update 更新/修改记录

mysql> update db01.t1 set id=5 where NAME='test01';mysql> update db01.t1 set id=6 where NAME='test02';mysql> update db01.t1 set id=7 where NAME='test03';

delete/truncate 删除和清空表

mysql> delete from mysql.user where user=''; －－删除mysql中的匿名用户mysql> flush privileges;mysql> create table t3 like t1; 复制表结构不复制数据mysql> insert into t3 select * from t1;mysql> delete from t3; --删除整个表,一行一行删除,所有的操作都会被记录至事务日志中mysql> insert into t3 select * from t1;mysql> delete from t3 where id=1; --指定条件删除mysql> truncate from t2 where id=2; --报错

查询语句 select--查询

通配符： % 匹配0个或任意多个字符 _ 匹配一个字符 ＝ 精确匹配 like 模糊匹配 regex(^ . .* .....) 使用正则表达式来匹配排序： order by 排序 asc 升序排列结果 desc 降序排列结果 group by 聚合 distinct 去除重复的行

mysql> use ceshi2mysql> create table ceshi2.t1(id int ,name varchar(50) ,math tinyint, english tinyint);mysql> insert into ceshi2.t1 set id=1,name='zhangsan',math=55,english=66;mysql> insert into ceshi2.t1 set id=2,name='lisi',math=66,english=77;mysql> insert into ceshi2.t1 set id=3,name='wangwu',math=65,english=30;mysql> insert into ceshi2.t1 set id=2,name='li04',math=88,english=99;mysql> insert into ceshi2.t1 set id=3,name='wang5',math=75,english=73;mysql> insert into ceshi2.t1 set id=4,name='zhao6',math=75,english=73;mysql> insert into ceshi2.t1 set id=5,name='liu3',math=85,english=43;mysql> select * from ceshi2.t1; --查询表中所有的列对应的值（全表扫描）mysql> select id,name from t1; --查询表中指定列mysql> select host,password,user from mysql.user; --查询表中指定列mysql> select host as '主机名',password as '密码',user as '用户名' from mysql.user; --给列取别名，增加可读性mysql> select * from t1 where name='i';mysql> select * from t1 where name like 'i';mysql> select * from t1 where name like '%i%'; --模糊匹配mysql> select * from t1 where name like '____';mysql> select * from t1 where id=2;mysql> select * from t1 where name='wang5'; --精确匹配mysql> select * from t1 where english < 60;mysql> select * from t1 where name regexp '.*[0-9]?.*' ; --支持正则表达式mysql> select * from t1 where name regexp '.*[0-9]+.*' ; 任意数字一次或一次以上mysql> select * from t1 where name regexp '.*[0-9]{2}.*' ;mysql> select user,password,host from mysql.user where host regexp '^l'; --支持正则表达式mysql> select user,password,host from mysql.user where host regexp '([0-9]{1,3}\.){3}([0-9]{1,3})';排序mysql> select * from t1 where name regexp '.*[0-9]?.*' order by id asc; 升序mysql> select * from t1 where name regexp '.*[0-9]?.*' order by id desc; 降序 去除重复行 distinctmysql> select distinct id from t1 ;聚合 group by 聚合以第一个为标准mysql> select * from t1 group by id;mysql> select * from t1 group by id having id <= 2;gruop by 不能用where语句 用having语句

分页函数(limint)指定只显示前几条数据

mysql> select * from t1 limit 10; --显示前10行mysql> select * from t1 limit 10,10; --显示11至20行mysql> select * from t1 limit 1; 显示第1行mysql> select * from t1 limit 0,2; 显示第1,2行mysql> select * from t1 limit 2,2; 显示3,4行起始位置，偏移量 第二行的下2行mysql> select * from t1 limit 4,2; 显示5,6行mysql> select * from t1 limit 6,2; 显示第七行

mysql> select * from t1 order by english desc limit 3;

显示英语前三名

mysql> select name,(math+english) as sum from t1 order by sum desc;

显示总分，以降序排列

mysql> select name,(math+english) as sum from t1 order by sum desc limit 1;

显示总分第一名

mysql> select name,max((math+english)) from t1;

显示总分第一名

mysql> select name,max(math+english) from t1 order by (math+english) desc;

显示总分第一名

mysql> select name,english from t1;

mysql> select max(english) from t1;

显示英语的最高分

mysql> select min(english) from t1;

显示英语的最低分

mysql> select max(english) from t1;

显示英语的最高分

mysql> select min(english) from t1;

显示英语的最低分

mysql> select name,english from t1 where english in (select max(english) from t1);

子查询

显示英语的最高分

* and or not 逻辑运算

1.and

mysql> select * from t1 where math >= 60 and english >= 60;

2.or

mysql> select * from t1 where math >= 60 or english >= 60; 其中一科及格

3.not

mysql> select * from t1 where math >= 60 and not english >= 60;

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

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

| 3 | wangwu | 65 | 30 |

| 5 | liu3 | 85 | 43 |

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

2 rows in set (0.00 sec)

* mysql常用函数 sum() avg() max() min() count()

mysql> select name,sum(math),sum(english) from t1;

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

| name | sum(math) | sum(english) |

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

| zhangsan | 215 | 252 |

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

1 row in set (0.00 sec)

mysql> select name,avg(math),avg(english) from t1;

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

| name | avg(math) | avg(english) |

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

| zhangsan | 53.7500 | 63.0000 |

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

1 row in set (0.00 sec)

mysql> select name,max(english) from t1;

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

| name | max(english) |

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

| zhangsan | 90 |

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

1 row in set (0.00 sec)

mysql> select name,min(english) from t1;

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

| name | min(english) |

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

| zhangsan | 33 |

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

1 row in set (0.00 sec)

mysql> select count() from t1;

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

| count() |

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

| 4 |

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

1 row in set (0.00 sec)

mysql> select max(english) - min(math) from t1; --英语的最高分与数学最低的差距

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

| max(english) - min(math) |

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

| 50 |

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

1 row in set (0.00 sec)

mysql> select * from t1 order by english desc limit 3;

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

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

| 1 | zhangsan | 70 | 90 |

| 4 | lisi02 | 55 | 69 |

| 2 | lisi | 50 | 60 |

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

3 rows in set (0.00 sec)

mysql> select * from t1 order by english asc limit 1,2; 显示第二名和第三名

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

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

| 4 | lisi02 | 55 | 69 |

| 2 | lisi | 50 | 60 |

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

2 rows in set (0.00 sec)

mysql> select * from ceshi1.t1 where math >= 60 or english >=60 ;

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

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

| 1 | zhangsan | 70 | 90 |

| 2 | lisi | 50 | 60 |

| 4 | lisi02 | 55 | 69 |

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

3 rows in set (0.00 sec)

* 复制表结构 表结构的复制

mysql> create table t3 like t1; --复制表结构

mysql> create database db03;

mysql> use db03

mysql> create table t1(id int,name varchar(50));

mysql> create table t2(id int,socre int);

mysql> insert into t1 set id=1,name='lee';

mysql> insert into t1 set id=2,name='zhang';

mysql> insert into t1 set id=4,name='wang';

mysql> insert into t2 set id=1,socre='90';

mysql> insert into t2 set id=2,socre='100';

mysql> insert into t2 set id=3,socre='90';

mysql> select * from t1;

* 列类型

整数

create table t1(id tinyint(2), name varchar(50))

· TINYINT[(M)] [UNSIGNED] [ZEROFILL] [not null] [comment]

很小的整数。带符号的范围是-128到127。无符号的范围是0到255。

· MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]

中等大小的整数。带符号的范围是-8388608到8388607。无符号的范围是0到16777215。

· INT[(M)] [UNSIGNED] [ZEROFILL]

普通大小的整数。带符号的范围是-2147483648到2147483647。无符号的范围是0到4294967295。

· INTEGER[(M)] [UNSIGNED] [ZEROFILL]

这是INT的同义词。

· BIGINT[(M)] [UNSIGNED] [ZEROFILL]

大整数。带符号的范围是-9223372036854775808到9223372036854775807。无符号的范围是0到18446744073709551615。

mysql> use db01

mysql> show tables;

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

| Tables_in_db01 |

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

| t1 |

| t2 |

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

2 rows in set (0.00 sec)

mysql> create table t4(id int ,name char(50),salary decimal(10,2));

mysql> desc t4;

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

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

| id | int(11) | YES | | NULL | |

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

3 rows in set (0.00 sec)

mysql> insert into t4 set id='test01' ,name='asdasdad',salary='dadadadasd' ;

Query OK, 1 row affected, 2 warnings (0.00 sec)

mysql> show warnings;

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

| Level | Code | Message |

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

| Warning | 1366 | Incorrect integer value: 'test01' for column 'id' at row 1 |

| Warning | 1366 | Incorrect decimal value: 'dadadadasd' for column 'salary' at row 1 |

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

2 rows in set (0.00 sec)

mysql> select * from t4;

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

| id | name | salary |

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

| 0 | asdasdad | 0.00 |

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

1 row in set (0.00 sec)

=============

mysql> create table t5(id tinyint);

Query OK, 0 rows affected (0.01 sec)

mysql> insert into t5 set id=-10;

Query OK, 1 row affected (0.00 sec)

mysql> select * from t5;

+------+

| id |

+------+

| -10 |

+------+

1 row in set (0.00 sec)

mysql> insert into t5 set id=-300;

Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> select * from t5;

+------+

| id |

+------+

| -10 |

| -128 |

+------+

2 rows in set (0.00 sec)

mysql> alter table t5 modify id tinyint unsigned;

mysql> insert t4 set id=2500;

Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select * from t5;

+------+

| id |

+------+

| 0 |

| 250 |

| 255 |

+------+

4 rows in set (0.00 sec)

浮点数 decimal指定小数点的位数

mysql> alter table t5 add salary decimal(7,2) unsigned after id;

mysql> update t5 set salary=1000000 where id=255;

mysql> select * from t5;

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

| id | salary |

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

| 0 | NULL |

| 250 | NULL |

| 255 | 999999.99 |

日期和时间类型概述

mysql> alter table t5 add date date;

mysql> alter table t5 add datetime datetime;

mysql> alter table t5 add time TIMESTAMP;

mysql> insert into t5(id,salary,date,datetime) values(1,10000,'2011-09-01','2011-09-01 11:28:01');

mysql> select * from t5;

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

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

| 1 | 10000.00 | 2011-09-01 11:28:27 | 2011-09-01 | 2011-09-01 11:28:01 |

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

1 row in set (0.00 sec)

写在最后:

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