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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