Mysql之SQL语句初级用法

前言

本文通过简单的示例去了解Mysql的DDL、DML、DCL的语句用法。

一、DDL语句

DDL（Data Definition Language）语句：数据定义语言，主要是进行定义/改变表的结构、数据类型、表之间的链接等操作。常用的语句关键字有 CREATE、DROP、ALTER 等。

获取帮助信息

mysql> HELP CREATE TABLE;

Name: 'CREATE TABLE'

Description:

Syntax:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    (create_definition,...)

    [table_options]

    [partition_options]

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    [(create_definition,...)]

    [table_options]

    [partition_options]

    [IGNORE | REPLACE]

    [AS] query_expression

...

创建数据库

mysql> CREATE DATABASE [IF NOT EXISTS] 'db_name';

mysql> SHOW DATABASES;

mysql> CREATE DATABASE IF NOT EXISTS dbtest;

Query OK, 1 row affected (0.00 sec)

mysql> SHOW DATABASES;

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

| Database           |

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

| information_schema |

| dbtest             |

| mysql              |

| performance_schema |

| sys                |

| test               |

| testdb             |

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

7 rows in set (0.00 sec)

创建表

CREATE TABLE [IF NOT EXISTS] 'tbl_name' (col1 type1, col2 type2, ...)

				col type1

				PRIMARY KEY(col1,...)

				INDEX(col1, ...)

				UNIQUE KEY(col1, ...)

创建一个表，id为主键

UNSIGNED:数值专用修饰符，表示无符号，不能表示负数，仅用于表示正数。

mysql> CREATE TABLE students (id int UNSIGNED NOT NULL primary key,name VARCHAR(20) NOT NULL,age tinyint UNSIGNED);

Query OK, 0 rows affected (0.02 sec)

mysql> DESC students;

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

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

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

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

| name  | varchar(20)         | NO   |     | NULL    |       |

| age   | tinyint(3) unsigned | YES  |     | NULL    |       |

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

3 rows in set (0.00 sec)

创建tbl2表，把id和name定义成主键

mysql> CREATE TABLE tbl2 (id int UNSIGNED NOT NULL,name VARCHAR(20) NOT NULL,age tinyint UNSIGNED,PRIMARY KEY(id,name));

Query OK, 0 rows affected (0.01 sec)

mysql> DESC tbl2;

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

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

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

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

| name  | varchar(20)         | NO   | PRI | NULL    |       |

| age   | tinyint(3) unsigned | YES  |     | NULL    |       |

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

3 rows in set (0.00 sec)

查看创建表时的命令

mysql> SHOW CREATE TABLE students;

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

| Table    | Create Table                                                                                                                                                                                   |

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

| students | CREATE TABLE `students` (

  `id` int(10) unsigned NOT NULL,

  `name` varchar(20) NOT NULL,

  `age` tinyint(3) unsigned DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

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

1 row in set (0.00 sec)

查看表的状态

mysql> SHOW TABLE STATUS LIKE 'students';

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

| Name     | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time         | Update_time | Check_time | Collation       | Checksum | Create_options | Comment |

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

| students | InnoDB |      10 | Dynamic    |    0 |              0 |       16384 |               0 |            0 |         0 |           NULL | 2024-03-03 21:47:36 | NULL        | NULL       | utf8_general_ci |     NULL |                |         |

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

1 row in set (0.00 sec)

mysql> SHOW TABLE STATUS LIKE 'students'\G

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

           Name: students

         Engine: InnoDB

        Version: 10

     Row_format: Dynamic

           Rows: 0

 Avg_row_length: 0

    Data_length: 16384

Max_data_length: 0

   Index_length: 0

      Data_free: 0

 Auto_increment: NULL

    Create_time: 2024-03-03 21:47:36

    Update_time: NULL

     Check_time: NULL

      Collation: utf8_general_ci

       Checksum: NULL

 Create_options:

        Comment:

1 row in set (0.00 sec)

删除表

DROP TABLE [IF EXISTS] 'tbl_name';
修改表

查看帮助信息

mysql> HELP ALTER TABLE;

Name: 'ALTER TABLE'

Description:

Syntax:

ALTER TABLE tbl_name

    [alter_specification [, alter_specification] ...]

    [partition_options]

alter_specification:

    table_options

  | ADD [COLUMN] col_name column_definition

        [FIRST | AFTER col_name]

  | ADD [COLUMN] (col_name column_definition,...)

  | ADD {INDEX|KEY} [index_name]

        [index_type] (key_part,...) [index_option] ...

  | ADD {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name]

        (key_part,...) [index_option] ...

  | ADD [CONSTRAINT [symbol]] PRIMARY KEY

        [index_type] (key_part,...)

        [index_option] ...

 ...

ALTER TABLE 'tbl_name'

  字段：

	 添加字段：add

		ADD col1 data_type [FIRST|AFTER col_name]

	 删除字段：drop

	 修改字段：alter, change, modify

  索引:

	 添加索引：add

	 删除索引: drop

  表选项

	 修改:

为students增加字段gender(性别)为枚举类型，放在最后

mysql> ALTER TABLE students ADD gender ENUM('m','f');

Query OK, 0 rows affected (0.07 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC students;

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

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

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

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

| name   | varchar(20)         | NO   |     | NULL    |       |

| age    | tinyint(3) unsigned | YES  |     | NULL    |       |

| gender | enum('m','f')       | YES  |     | NULL    |       |

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

4 rows in set (0.00 sec)

修改students表的id字段名称为sid，修改名称一定要定义字段属性否则会使用默认值

mysql> ALTER TABLE students CHANGE id sid int UNSIGNED NOT NULL;

Query OK, 0 rows affected (0.00 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC students;

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

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

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

| sid    | int(10) unsigned    | NO   | PRI | NULL    |       |

| name   | varchar(20)         | NO   |     | NULL    |       |

| age    | tinyint(3) unsigned | YES  |     | NULL    |       |

| gender | enum('m','f')       | YES  |     | NULL    |       |

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

4 rows in set (0.00 sec)

修改name字段为唯一键

mysql>  ALTER TABLE students ADD UNIQUE KEY(name);

Query OK, 0 rows affected (0.01 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC students;

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

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

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

| sid    | int(10) unsigned    | NO   | PRI | NULL    |       |

| name   | varchar(20)         | NO   | UNI | NULL    |       |

| age    | tinyint(3) unsigned | YES  |     | NULL    |       |

| gender | enum('m','f')       | YES  |     | NULL    |       |

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

4 rows in set (0.00 sec)

添加索引

mysql> ALTER TABLE students ADD  INDEX(age);

Query OK, 0 rows affected (0.01 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC students;

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

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

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

| sid    | int(10) unsigned    | NO   | PRI | NULL    |       |

| name   | varchar(20)         | NO   | UNI | NULL    |       |

| age    | tinyint(3) unsigned | YES  | MUL | NULL    |       |

| gender | enum('m','f')       | YES  |     | NULL    |       |

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

4 rows in set (0.00 sec)

查看表上的索引

students表中有三个索引

主键：sid

唯一键：name

普通索引：age

mysql> SHOW INDEXES FROM students;

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

| Table    | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

| students |          0 | PRIMARY  |            1 | sid         | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |

| students |          0 | name     |            1 | name        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |

| students |          1 | age      |            1 | age         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |

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

3 rows in set (0.00 sec)

删除索引

mysql> ALTER TABLE students DROP age;

Query OK, 0 rows affected (0.03 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW INDEXES FROM students;

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

| Table    | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

| students |          0 | PRIMARY  |            1 | sid         | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |

| students |          0 | name     |            1 | name        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |

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

2 rows in set (0.01 sec)

创建索引可以在表中定义也可以单独创建

创建索引：

  CREATE INDEX index_name ON tbl_name (index_col_name,...);

删除索引：

  DROP INDEX index_name ON tbl_name;

mysql> DROP INDEX name ON students;

Query OK, 0 rows affected (0.04 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW INDEXES FROM students;

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

| Table    | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

| students |          0 | PRIMARY  |            1 | sid         | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |

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

1 row in set (0.00 sec)

二、DML语句

DML（Data Manipulation Language）语句: 数据操纵语言，主要是对数据进行增加、删除、修改操作。常用的语句关键字有 INSERT、UPDATE、DELETE 等。

INSERT(REPLACE)、DELETE、UPDATE、SELECT

查看帮助信息

mysql> HELP INSERT;

Name: 'INSERT'

Description:

Syntax:

INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]

    [INTO] tbl_name

    [PARTITION (partition_name [, partition_name] ...)]

    [(col_name [, col_name] ...)]

    {VALUES | VALUE} (value_list) [, (value_list)] ...

    [ON DUPLICATE KEY UPDATE assignment_list]

...

向表中插入数据

mysql> INSERT INTO students VALUES (1,'Yang Guo','m'),(2,'Guo xiang','f');

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM students;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

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

2 rows in set (0.00 sec)

mysql> INSERT INTO students (sid,name) VALUES (3,'ZHANG Wuji'),(4,'Zhao Min');

Query OK, 2 rows affected (0.01 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM students;

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

| sid | name       | gender |

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

|   1 | Yang Guo   | m      |

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

4 rows in set (0.00 sec)

查询数据通过条件

mysql> mysql> SELECT * FROM students WHERE sid<3;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

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

2 rows in set (0.00 sec)

mysql> SELECT * FROM students WHERE gender='m';

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

| sid | name     | gender |

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

|   1 | Yang Guo | m      |

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

1 row in set (0.00 sec)

mysql> SELECT * FROM students WHERE gender='';

Empty set (0.00 sec)

mysql> SELECT * FROM students WHERE gender IS NOT NULL;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

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

2 rows in set (0.00 sec)

mysql> SELECT * FROM students WHERE gender IS  NULL;

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

| sid | name       | gender |

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

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

2 rows in set (0.00 sec)

查找数据并排序

mysql> SELECT * FROM students ORDER BY name;

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

| sid | name       | gender |

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

|   2 | Guo xiang  | f      |

|   1 | Yang Guo   | m      |

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

4 rows in set (0.00 sec)

mysql> SELECT * FROM students ORDER BY name DESC;

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

| sid | name       | gender |

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

|   4 | Zhao Min   | NULL   |

|   3 | ZHANG Wuji | NULL   |

|   1 | Yang Guo   | m      |

|   2 | Guo xiang  | f      |

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

4 rows in set (0.00 sec)

查找数据并限制数量

mysql> SELECT * FROM students;

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

| sid | name       | gender |

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

|   1 | Yang Guo   | m      |

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

4 rows in set (0.00 sec)

查找2个

mysql> SELECT * FROM students LIMIT 2;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

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

2 rows in set (0.00 sec)

1,2 把第一个略过，查找2个

mysql> SELECT * FROM students   LIMIT 1,2;

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

| sid | name       | gender |

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

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

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

2 rows in set (0.00 sec)

查询大于等于2小于等于4

mysql> SELECT * FROM students WHERE sid>=2 and sid<=4;

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

| sid | name       | gender |

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

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

3 rows in set (0.00 sec)

mysql> SELECT * FROM students WHERE sid BETWEEN 2 AND 4;

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

| sid | name       | gender |

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

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

3 rows in set (0.00 sec)

Like查找数据

mysql> SELECT * FROM students WHERE name LIKE 'Z%';

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

| sid | name       | gender |

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

|   3 | ZHANG Wuji | NULL   |

|   4 | Zhao Min   | NULL   |

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

2 rows in set (0.00 sec)

基于正则表达式模式匹配

mysql> SELECT * FROM students WHERE name RLIKE '.*u.*';

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

| sid | name       | gender |

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

|   1 | Yang Guo   | m      |

|   2 | Guo xiang  | f      |

|   3 | ZHANG Wuji | NULL   |

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

3 rows in set (0.00 sec)

mysql> SELECT * FROM students WHERE name RLIKE '.*[A-G]u.*';

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

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

2 rows in set (0.00 sec)

字段别名

mysql> SELECT sid as stuid,name as stuname FROM students;

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

| stuid | stuname    |

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

|     1 | Yang Guo   |

|     2 | Guo xiang  |

|     3 | ZHANG Wuji |

|     4 | Zhao Min   |

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

4 rows in set (0.00 sec)

删除数据

删除数据的时候一定指定条件，否则所有字段全部删除

mysql> DELETE FROM students WHERE sid=3;

Query OK, 1 row affected (0.06 sec)

mysql> SELECT * FROM students;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

|   4 | Zhao Min  | NULL   |

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

3 rows in set (0.00 sec)

更新表中的数据

mysql> UPDATE students SET gender='f' WHERE sid=4;

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM students;

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

| sid | name      | gender |

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

|   1 | Yang Guo  | m      |

|   2 | Guo xiang | f      |

|   4 | Zhao Min  | f      |

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

3 rows in set (0.00 sec)

三、DCL

DCL（Data Control Language）语句：数据控制语言，主要是用来设置/更改数据库用户权限。常用关键字有 GRANT、REVOKE 等。

创建用户账号

创建用户账号：

  CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];

删除用户：

  DROP USER 'username'@'host';

mysql> CREATE USER 'wpuwer'@'%' IDENTIFIED BY 'wppass';

Query OK, 0 rows affected (0.00 sec)

mysql> USE mysql;

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

mysql> SELECT User,Host FROM user;

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

| User          | Host      |

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

| cdbsync       | %         |

| dsmart        | %         |

| root          | %         |

| wpuwer        | %         |

| mysql.session | localhost |

| mysql.sys     | localhost |

| root          | localhost |

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

7 rows in set (0.00 sec)

授权用户testuser访问testdb的所有表，并创建用户testuser

mysql> GRANT SELECT,DELETE ON testdb.* TO 'testuser'@'%' IDENTIFIED BY 'testpass';

Query OK, 0 rows affected, 1 warning (0.01 sec)

查看用户授权

SHOW GRANTS FOR 'user'@'host'; 

mysql> SHOW GRANTS FOR 'wpuwer'@'%';

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

| Grants for wpuwer@%                |

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

| GRANT USAGE ON *.* TO 'wpuwer'@'%' |

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

1 row in set (0.00 sec)

查看当前用户授权

mysql> SHOW GRANTS FOR CURRENT_USER;

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

| Grants for root@localhost                                           |

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

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

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

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

2 rows in set (0.00 sec)

回收用户testuser在testdb的所有表的delete权限

mysql> REVOKE DELETE ON testdb.* FROM 'testuser'@'%';

Query OK, 0 rows affected (0.00 sec)

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