SQL使用

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)：

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：

创建数据库：

mysql> create database ceshi1; #创建数据库ceshi1
Query 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-8
Query 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

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 changed
mysql> 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50
3. 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50
mysql> 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
# 之后将被修改为 SET PASSWORD FOR <user> = '<plaintext_password>'
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                      | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257

mysql> 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)

删除表/库：

删除表/库  
mysql> use ceshi1 
mysql> 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 tables
mysql> 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

修改数据库：

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：

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id2
mysql> 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

mysql> truncate t2;                                     --一次性全部删除,不会被记录至事务日志中.

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
- regexp(^ . .* .....)：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。
聚合函数：

函数	作用
COUNT	计算表中的记录（行数）
SUM	计算表中数值列的数据合计值
AVG	计算表中数值列的数据平均值
MAX	求出表中任意列中数据的最大值
MIN	求出表中任意列中数据的最小值

查找案例：

    mysql> select  * from t1  id;

    mysql> select * from t1  id having id <= 2;="" gruop="" by="" 不能用where语句="" 用having语句="" mysql=""> use ceshi2
    mysql> 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 distinct
    mysql> 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

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 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： ```shell 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;
+------+--------+------+---------+
| id   | name   | math | english |
+------+--------+------+---------+
|    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()： ```shell 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;
+------+----------+------+---------+
| id   | name     | math | english |
+------+----------+------+---------+
|    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
+------+--------+------+---------+
| id   | name   | math | english |
+------+--------+------+---------+
|    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 ;
+------+----------+------+---------+
| id   | name     | math | english |
+------+----------+------+---------+
|    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;
 mysql> select * from t1,t2;      笛卡尔集,2张表的乘方 
 +------+-------+------+-------+
 | id   | name  | id   | socre |
 +------+-------+------+-------+
 |    1 | lee   |    1 |    90 |
 |    2 | zhang |    1 |    90 |
 |    4 | wang  |    1 |    90 |
 |    1 | lee   |    2 |   100 |
 |    2 | zhang |    2 |   100 |
 |    4 | wang  |    2 |   100 |
 |    1 | lee   |    3 |    90 |
 |    2 | zhang |    3 |    90 |
 |    4 | wang  |    3 |    90 |
 +------+-------+------+-------+
 9 rows in set (0.00 sec)

 mysql>create table db03.t3 (id int,name varchar(50));
 mysql> insert into t3 select * from t1; --复制记录
 mysql> select * from t3;
 +------+-------+
 | id   | name  |
 +------+-------+
 |    1 | lee   |
 |    2 | zhang |
 |    4 | wang  |
 +------+-------+
 3 rows in set (0.00 sec)

 多表查询
 mysql> select t1.id,t1.name,t2.socre from t1,t2 where t1.id=t2.id;
 +------+-------+-------+
 | id   | name  | socre |
 +------+-------+-------+
 |    1 | lee   |    90 |
 |    2 | zhang |   100 |
 +------+-------+-------+
 2 rows in set (0.00 sec)

表的连接:纵向连接/内连接/左连接/右连接：

```shell 常规查表: mysql> select from t1,t2; mysql> select from t1,t2 where t1.id=t2.id; +------+-------+------+-------+ | id | name | id | socre | +------+-------+------+-------+ | 1 | lee | 1 | 90 | | 2 | zhang | 2 | 100 | +------+-------+------+-------+ 2 rows in set (0.00 sec)

左连接（以左表为标准连接右表）: letft join=left [outer] join

mysql> select * from t1 left outer join t2 ON t1.id=t2.id; +------+-------+------+-------+ | id | name | id | socre | +------+-------+------+-------+ | 1 | lee | 1 | 90 | | 2 | zhang | 2 | 100 | | 4 | wang | NULL | NULL | +------+-------+------+-------+ 3 rows in set (0.00 sec)

右连接（以右表为标准连接左表）:
right join= right outer join
mysql> select * from t1 right outer join t2 ON t1.id=t2.id;
+------+-------+------+-------+
| id   | name  | id   | socre |
+------+-------+------+-------+
|    1 | lee   |    1 |    90 |
|    2 | zhang |    2 |   100 |
| NULL | NULL  |    3 |    90 |
+------+-------+------+-------+
3 rows in set (0.00 sec)


内连接:取多表之间的交集
mysql> select * from t1 inner join t2 on t1.id=t2.id;
+------+-------+------+-------+
| id   | name  | id   | socre |
+------+-------+------+-------+
|    1 | lee   |    1 |    90 |
|    2 | zhang |    2 |   100 |
+------+-------+------+-------+
2 rows in set (0.00 sec)

纵向连接:
mysql> select * from t1 union select * from t2;
+------+-------+
| id   | name  |
+------+-------+
|    1 | lee   |
|    2 | zhang |
|    4 | wang  |
|    1 | 90    |
|    2 | 100   |
|    3 | 90    |
+------+-------+
6 rows in set (0.00 sec)
```

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。
大整数。带符号的范围是-9223372036854775808到9223372036854775807。无符号的范围是0到18446744073709551615。
```
BIGINT[(M)] [UNSIGNED] [ZEROFILL]
```

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;
+--------+---------------+------+-----+---------+-------+
| Field  | Type          | Null | Key | Default | Extra |
+--------+---------------+------+-----+---------+-------+
| id     | int(11)       | YES  |     | NULL    |       |
| name   | char(50)      | YES  |     | NULL    |       |
| salary | decimal(10,2) | 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 |
|    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 |
|    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;
+------+----------+---------------------+------------+---------------------+
| id   | salary   | time                | date       | datetime            |
+------+----------+---------------------+------------+---------------------+
|    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)
```

MySQL之SQL语句的使用