SQL是Structure Query Language(结构化查询语言）的缩写，它是关系型数据库的应用语言，由IBM在20世纪70年×××发，以实现关系型数据库中的信息检索。

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    在20世纪80年代初，美国国家标准局（ANSI)开始着手制定SQL标准，最早的ANSI标准于1986年完成，就被叫做SQL-86。正是由于SQL语言的标准化，所以大多数关系型数据库都支持SQL语言，它已经发展成为多种平台进行交互操作的底层会话语言。

    SQL的分类：

• DDL：数据定义语言，即是对数据库内部对象进行创建、删除、修改等操作的语言，和DML最大区别在于DML仅对表内数据进行操作，而不涉及到表的定义、结构的修改，更不会涉及其它对象，DBA使用较多。常用关键字包括create、drop、alter等。

• DML：数据操作语言，用于添加、删除、更新和查询表中的记录，并检查数据的完整性，开发人员使用较多。常用的语句包括insert、delete、update、和select等。

• DCL：数据控制语言，用于管理系统中的对象权限时使用，常用语句有grant、revoke等。

1 DDL语句示例：

1）创建数据库

MySQL> show engines;                        #查看支持的引擎，包括默认的引擎

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

| Engine     | Support | Comment                                                    | Transactions | XA   | Savepoints |

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

| MRG_MYISAM | YES     | Collection of identical MyISAM tables                      | NO           | NO   | NO         |

| CSV        | YES     | CSV storage engine                                         | NO           | NO   | NO         |

| MyISAM     | DEFAULT | Default engine as of MySQL 3.23 with great performance     | NO           | NO   | NO         |

| InnoDB     | YES     | Supports transactions, row-level locking, and foreign keys | YES          | YES  | YES        |

| MEMORY     | YES     | Hash based, stored in memory, useful for temporary tables  | NO           | NO   | NO         |

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

mysql> show character set;                   #查看系统支持的字符集

mysql> show variables like "character%";     #查看当前字符集设置

mysql> show variables like "collation%";     #查看字符集校验设置

mysql> create database test1;                #创建test1数据库

Query OK, 1 row affected (0.05 sec)

mysql> show databases;                       #查看数据库

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

| Database           |

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

| information_schema |

| mysql              |

| performance_schema |

| test               |

| test1              |

| testdb             |

mysql> create database t121 default character set utf8 collate utf8_general_ci;

Query OK, 1 row affected (0.00 sec)          #创建时，也可以指定字符集

2）删除数据库

mysql> drop database test1;

Query OK, 0 rows affected (0.01 sec)

mysql> show databases;

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

| Database           |

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

| information_schema |

| mysql              |

| performance_schema |

| test               |

| testdb             |

备注：数据库一旦被删除，库中所有的表也将被删除，因此，备份非常重要

3）创建表

mysql> use zwj;                              #选择数据库

mysql> create table emp                      #varchar(n)其中n代表字符数

    -> (ename varchar(10),

    -> hiredate date,

    -> sal decimal(10,2),

    -> deptno int(2));

Query OK, 0 rows affected (0.11 sec)

mysql> desc zwj.emp;                        #查看zwj库中的emp表的结构

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

| Field    | Type          | Null | Key | Default | Extra |

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

| ename    | varchar(10)   | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

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

mysql> show create table zwj.emp\g          #查看创建表的SQL语句，包括使用的字符集

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

| Table | Create Table                                                                                                                                                                                     |

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

| emp   | CREATE TABLE `emp` (

  `ename` varchar(10) DEFAULT NULL,

  `hiredate` date DEFAULT NULL,

  `sal` decimal(10,2) DEFAULT NULL,

  `deptno` int(2) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

复制一张表

mysql> create table t119 like zwj.t118;

Query OK, 0 rows affected (0.04 sec)

mysql> insert into t119 select * from zwj.t118;

Query OK, 12 rows affected (0.00 sec)

Records: 12  Duplicates: 0  Warnings: 0

查看表的状态，了解两张表是否一致

mysql> use zwj;

Database changed

mysql> show table status\G

*************************** 1. row ***************************

           Name: t118

         Engine: MyISAM

        Version: 10

     Row_format: Fixed

           Rows: 12

 Avg_row_length: 30

    Data_length: 360

Max_data_length: 8444249301319679

   Index_length: 1024

      Data_free: 0

 Auto_increment: NULL

    Create_time: 2017-04-29 08:20:18

    Update_time: 2017-04-29 08:29:50

     Check_time: NULL

      Collation: latin1_swedish_ci

       Checksum: NULL

 Create_options: 

        Comment: 

*************************** 2. row ***************************

           Name: t119

         Engine: MyISAM

        Version: 10

     Row_format: Fixed

           Rows: 12

 Avg_row_length: 30

    Data_length: 360

Max_data_length: 8444249301319679

   Index_length: 1024

      Data_free: 0

 Auto_increment: NULL

    Create_time: 2017-04-29 09:09:12

    Update_time: 2017-04-29 09:09:38

     Check_time: NULL

      Collation: latin1_swedish_ci

       Checksum: NULL

 Create_options: 

        Comment: 

2 rows in set (0.00 sec)

查看指定表的状态信息

mysql> show table status like 't118'\G

*************************** 1. row ***************************

           Name: t118

         Engine: MyISAM

        Version: 10

     Row_format: Fixed

           Rows: 12

 Avg_row_length: 30

    Data_length: 360

Max_data_length: 8444249301319679

   Index_length: 1024

      Data_free: 0

 Auto_increment: NULL

    Create_time: 2017-04-29 08:20:18

    Update_time: 2017-04-29 08:29:50

     Check_time: NULL

      Collation: latin1_swedish_ci

       Checksum: NULL

 Create_options: 

        Comment: 

1 row in set (0.00 sec)

4）删除表

mysql> drop table zwj.emp;

Query OK, 0 rows affected (0.05 sec)

5）修改表，需要用到alter table语句

修改表ename字段的定义，把varchar(10)改为varchar(20)

mysql> alter table emp modify ename varchar(20);    #关键字modify用于修改表中字段的定义

Query OK, 0 rows affected (0.17 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;

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

| Field    | Type          | Null | Key | Default | Extra |

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

| ename    | varchar(20)   | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

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

在表emp中新增字段age，类型为int(3):

mysql> alter table emp add age int(3);                #默认排在最后

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;

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

| Field    | Type          | Null | Key | Default | Extra |

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

| ename    | varchar(20)   | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

| age      | int(3)        | YES  |     | NULL    |       |

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

5 rows in set (0.00 sec)

删除一个字段

mysql> alter table emp drop age;

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

修改字段名称

mysql> alter table emp change age age1 int(4);    #关键字change可以修改表的定义，如字段名

Query OK, 0 rows affected (0.03 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;

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

| Field    | Type          | Null | Key | Default | Extra |

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

| ename    | varchar(20)   | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

| age1     | int(4)        | YES  |     | NULL    |       |

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

修改字段排列顺序

mysql> alter table emp add birth date after ename;    #新增字段birth，排在ename之后

Query OK, 0 rows affected (0.08 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;

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

| Field    | Type          | Null | Key | Default | Extra |

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

| ename    | varchar(20)   | YES  |     | NULL    |       |

| birth    | date          | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

| age1     | int(4)        | YES  |     | NULL    |       |

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

6 rows in set (0.00 sec)

把字段deptno放在age1后面

mysql> alter table emp1 modify deptno int(2) after age1;

Query OK, 0 rows affected (0.14 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp1;

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

| Field  | Type        | Null | Key | Default | Extra |

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

| age1   | int(4)      | YES  |     | NULL    |       |

| deptno | int(2)      | YES  |     | NULL    |       |

| ename  | varchar(20) | YES  |     | NULL    |       |

| birth  | date        | YES  |     | NULL    |       |

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

4 rows in set (0.00 sec)

把字段age1放在最前面

mysql> alter table emp modify age1 int(4) first;

Query OK, 0 rows affected (0.15 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;

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

| Field    | Type          | Null | Key | Default | Extra |

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

| age1     | int(4)        | YES  |     | NULL    |       |

| ename    | varchar(20)   | YES  |     | NULL    |       |

| birth    | date          | YES  |     | NULL    |       |

| hiredate | date          | YES  |     | NULL    |       |

| sal      | decimal(10,2) | YES  |     | NULL    |       |

| deptno   | int(2)        | YES  |     | NULL    |       |

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

修改表名：

mysql> alter table emp rename emp1;

Query OK, 0 rows affected (0.02 sec)

mysql> show tables;

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

| Tables_in_zwj |

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

| emp1          |

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

1 row in set (0.00 sec)

2 DML语句示例

1）插入记录

mysql> insert into emp1(age1,ename,birth,deptno) values('555','aaa','2016-10-30','5');

Query OK, 1 row affected (0.03 sec)

也可以不指定字段名称，但values后面的顺序应该和字段的排列顺序一致

mysql> insert into emp1 values('666','bbb','2016-12-30','8');

mysql> select * from emp1;

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

| age1 | ename | birth      | deptno |

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

|  555 | aaa   | 2016-10-30 |      5 |

|  666 | bbb   | 2016-12-30 |      8 |

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

一次插入多条记录

mysql> insert into emp1(age1,ename,birth,deptno) 

    -> values ('111','ccc','2011-11-30','4'),

    -> ('666','ddd','2014-12-22','11'),

    -> ('888','eee','2015-11-30','22'),

    -> ('333','fff','2011-04-30','8');

Query OK, 4 rows affected (0.02 sec)

Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from emp1;

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

| age1 | ename | birth      | deptno |

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

|  555 | aaa   | 2016-10-30 |      5 |

|  666 | bbb   | 2016-12-30 |      8 |

|  111 | ccc   | 2011-11-30 |      4 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

|  333 | fff   | 2011-04-30 |      8 |

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

6 rows in set (0.00 sec)

2）更新记录，通过update命令进行更改

mysql> update emp1 set age1=1000 where ename='aaa';

Query OK, 1 row affected (0.03 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp1;

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

| age1 | ename | birth      | deptno |

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

| 1000 | aaa   | 2016-10-30 |      5 |

|  666 | bbb   | 2016-12-30 |      8 |

|  111 | ccc   | 2011-11-30 |      4 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

|  333 | fff   | 2011-04-30 |      8 |

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

6 rows in set (0.00 sec)

3）删除记录：

mysql> delete from emp1 where ename='bbb';

Query OK, 1 row affected (0.02 sec)

mysql> select * from emp1;

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

| age1 | deptno | ename | birth      |

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

|  111 |      4 | ccc   | 2011-11-30 |

|  666 |     11 | ddd   | 2014-12-22 |

|  888 |     22 | eee   | 2015-11-30 |

|  333 |      8 | fff   | 2011-04-30 |

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

4 rows in set (0.00 sec)

4）查询记录

mysql> select age1,ename from zwj.emp1;

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

| age1 | ename |

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

|  666 | bbb   |

|  111 | ccc   |

|  666 | ddd   |

|  888 | eee   |

|  333 | fff   |

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

把表中的记录去掉重复后显示出来，

mysql> select distinct age1 from emp1;        #distinct是关键字，age1是字段名

条件查询

mysql> select * from emp1 where age1='666';

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

| age1 | ename | birth      | deptno |

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

|  666 | bbb   | 2016-12-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

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

组合条件查询：

mysql> select * from emp1 where ename='bbb' and birth<'2017-01-01';

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

| age1 | ename | birth      | deptno |

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

|  666 | bbb   | 2016-12-30 |      8 |

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

mysql> select * from emp1 where ename='bbb' or birth<'2017-01-30';

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

| age1 | ename | birth      | deptno |

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

|  666 | bbb   | 2016-12-30 |      8 |

|  111 | ccc   | 2011-11-30 |      4 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

|  333 | fff   | 2011-04-30 |      8 |

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

5 rows in set (0.00 sec)

模式匹配：

mysql> select * from zwj.emp1 where ename regexp '^c';    #关键字regexp支持正则表达式

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

| age1 | deptno | ename | birth      |

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

|  111 |      4 | ccc   | 2011-11-30 |

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

1 row in set (0.00 sec)

mysql> select * from zwj.emp1 where ename like 'c_c';     #短横表示匹配任意单个字符

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

| age1 | deptno | ename | birth      |

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

|  111 |      4 | ccc   | 2011-11-30 |

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

1 row in set (0.01 sec)

mysql> select * from zwj.emp1 where ename like 'c%';     #%表示任意字符

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

| age1 | deptno | ename | birth      |

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

|  111 |      4 | ccc   | 2011-11-30 |

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

1 row in set (0.00 sec)

排序和限制：关键字order by（默认升序排序）

mysql> select * from emp1 order by age1;

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

| age1 | ename | birth      | deptno |

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

|  111 | ccc   | 2011-11-30 |      4 |

|  333 | fff   | 2011-04-30 |      8 |

|  666 | bbb   | 2016-12-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

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

5 rows in set (0.00 sec)

对age1相同的记录，如果把字段deptno从高到低排列，可使用如下命令，desc表示降序。

mysql> select * from emp1 order by age1,deptno desc;

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

| age1 | ename | birth      | deptno |

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

|  111 | ccc   | 2011-11-30 |      4 |

|  333 | fff   | 2011-04-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

|  666 | bbb   | 2016-12-30 |      8 |

|  888 | eee   | 2015-11-30 |     22 |

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

5 rows in set (0.01 sec)

对age1相同的记录，如果把字段deptno从低到高排列，可使用如下命令，asc表示升序。

mysql> select * from emp1 order by age1,deptno asc;

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

| age1 | ename | birth      | deptno |

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

|  111 | ccc   | 2011-11-30 |      4 |

|  333 | fff   | 2011-04-30 |      8 |

|  666 | bbb   | 2016-12-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

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

5 rows in set (0.01 sec)

选择排序后的前3条记录

mysql> select * from emp1 order by age1 limit 3;

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

| age1 | ename | birth      | deptno |

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

|  111 | ccc   | 2011-11-30 |      4 |

|  333 | fff   | 2011-04-30 |      8 |

|  666 | bbb   | 2016-12-30 |      8 |

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

3 rows in set (0.00 sec)

降序排列后的前3条记录

mysql> select * from emp1 order by age1 desc limit 3;

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

| age1 | ename | birth      | deptno |

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

|  888 | eee   | 2015-11-30 |     22 |

|  666 | bbb   | 2016-12-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

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

3 rows in set (0.00 sec)

显示以age1字段排序后，从第2条记录开始的前4条记录

mysql> select * from emp1 order by age1 limit 1,4;

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

| age1 | ename | birth      | deptno |

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

|  333 | fff   | 2011-04-30 |      8 |

|  666 | bbb   | 2016-12-30 |      8 |

|  666 | ddd   | 2014-12-22 |     11 |

|  888 | eee   | 2015-11-30 |     22 |

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

4 rows in set (0.00 sec)

3 DCL语句示例：

新建用户并且授权

mysql> grant select,insert on mysql.* to 'abc'@'localhost' identified by 'abc';

Query OK, 0 rows affected (0.08 sec)

撤消权限

mysql> revoke insert on mysql.* from 'abc'@'localhost';

Query OK, 0 rows affected (0.00 sec)

查看当前用户权限

mysql> show grants;

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

| Grants for root@localhost                                           |

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

| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |

| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION        |

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

查看某个用户权限

mysql> show grants for 'abc'@'localhost';

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

| Grants for abc@localhost                                                                                   |

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

| GRANT USAGE ON *.* TO 'abc'@'localhost' IDENTIFIED BY PASSWORD '*0D3CED9BEC10A777AEC23CCC353A8C08A633045E' |

| GRANT SELECT ON `mysql`.* TO 'abc'@'localhost'                                                             |

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

2 rows in set (0.00 sec)

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