MYSQL基础（sql语句）

SQL语句

SQL语句的多种类型：

1. 数据查询语言（DQL）
   数据查询语言（Data Query Language, DQL）是SQL语言中，负责进行数据查询而不会对数据本身进行修改的语句，这是最基本的SQL语句。SELECT是DQL（也是所有SQL）用得最多的动词，其他DQL常用的保留字有FROM，WHERE，GROUP BY，HAVING和ORDER BY。这些DQL保留字常与其他类型的SQL语句一起使用。
2. 数据定义语言（DDL）
   数据定义语言 (Data Definition Language, DDL) 是SQL语言集中，负责数据结构定义与数据库对象定义的语言，由CREATE、ALTER与DROP三个语法所组成。
3. 数据操纵语言（DML）
   数据操纵语言（Data Manipulation Language, DML）是SQL语言中，负责对数据库对象运行数据访问工作的指令集，以INSERT、UPDATE、DELETE三种指令为核心，分别代表插入、更新与删除。
4. 数据控制语言（DCL）
   数据控制语言 (Data Control Language) 在SQL语言中，是一种可对数据访问权进行控制的指令，它可以控制特定用户账户对数据表、查看表、预存程序、用户自定义函数等数据库对象的控制权。由GRANT和REVOKE两个指令组成。DCL以控制用户的访问权限为主，GRANT为授权语句，对应的REVOKE是撤销授权语句。
5. 指针控制语言（CCL）
   它的语句，像DECLARE CURSOR，FETCH INTO和UPDATE WHERE CURRENT用于对一个或多个表单独行的操作。
6. 事务处理语言（TPL）
   它的语句能确保被DML语句影响的表的所有行及时得以更新。TPL语句包括BEGIN TRANSACTION，COMMIT和ROLLBACK。

1、DDL操作

1.1 数据库DDL操作

//创建数据库
//语法：CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';

//创建数据库DNP
mysql> CREATE DATABASE IF NOT EXISTS DNP;
Query OK, 1 row affected (0.00 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| DNP                |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)


//删除数据库
//语法：DROP DATABASE [IF EXISTS] 'DB_NAME';

//删除数据库DNP
mysql> CREATE DATABASE IF NOT EXISTS DNP;
Query OK, 1 row affected (0.00 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| DNP                |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> DROP DATABASE IF EXISTS DNP;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

//创建数据库时,设置数据库的字符集：
//CHARACTER SET:指定数据库采用的字符集,utf8不能写成utf-8,建议使用utf8mb4字符集
//COLLATE:指定数据库字符集的排序规则,utf8mb4的默认排序规则为utf8mb4_general_ci（通过show character set查看）
mysql> CREATE DATABASE dbtest CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;

//数据库客户端字符编码需要和服务端字符集保持一致
//SET NAMES:指定客户端字符集
mysql> SET NAMES utf8mb4;

//字符集配置都可写入MySQL配置文件中启动MySQL服务时自动加载

1.2 表DDL操作

//创建表
//语法：CREATE TABLE table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型';

//在数据库dnp里创建表dunianpei
mysql> CREATE DATABASE dnP;
Query OK, 1 row affected (0.00 sec)

mysql> use dnP;
Database changed

//创建dunianpei表

mysql> CREATE TABLE dunianpei (id int(50) NOT NULL,name VARCHAR(120) NOT NULL,age tinyint);
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;  //查看当前数据库有哪些表
+---------------+
| Tables_in_dnP |
+---------------+
| dunianpei     |
+---------------+
1 row in set (0.00 sec)

//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';


//删除表dunianpei
mysql> DROP TABLE dunianpei;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
Empty set (0.00 sec

1.3 用户DDL操作

MySQL用户帐号由两部分组成，如’USERNAME’@‘HOST’，表示此USERNAME只能从此HOST上远程登录；HOST用于限制此用户可通过哪些主机远程连接mysql程序。

HOST的值可为：

• IP地址，如：192.168.48.151
• 通配符
  • %：匹配任意长度的任意字符，常用于设置允许从任何主机登录
  • _：匹配任意单个字符

//数据库用户创建
//语法：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];

//创建数据库用户dnp
mysql> CREATE USER 'dnp'@'127.0.0.1' IDENTIFIED BY 'dnp123456.';
Query OK, 0 rows affected (0.00 sec)

//刷新授权表
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

//使用新创建的用户和密码登录
[root@localhost ~]# mysql -udnp -pdnp123456. -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.37 MySQL Community Server (GPL)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

//删除数据库用户
//语法：DROP USER 'username'@'host'; 

//删除数据库用户dnp
mysql> DROP USER 'dnp'@'127.0.0.1';
Query OK, 0 rows affected (0.00 sec)

//刷新授权表
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

1.4 查看命令SHOW

mysql> SHOW CHARACTER SET;  //查看支持的所有字符集
+----------+---------------------------------+---------------------+--------+
| Charset  | Description                     | Default collation   | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese        | big5_chinese_ci     |      2 |
| dec8     | DEC West European               | dec8_swedish_ci     |      1 |
| cp850    | DOS West European               | cp850_general_ci    |      1 |
| hp8      | HP West European                | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian           | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European            | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European     | latin2_general_ci   |      1 |
| swe7     | 7bit Swedish                    | swe7_swedish_ci     |      1 |
| ascii    | US ASCII                        | ascii_general_ci    |      1 |
| ujis     | EUC-JP Japanese                 | ujis_japanese_ci    |      3 |
| sjis     | Shift-JIS Japanese              | sjis_japanese_ci    |      2 |
| hebrew   | ISO 8859-8 Hebrew               | hebrew_general_ci   |      1 |
| tis620   | TIS620 Thai                     | tis620_thai_ci      |      1 |
| euckr    | EUC-KR Korean                   | euckr_korean_ci     |      2 |
| koi8u    | KOI8-U Ukrainian                | koi8u_general_ci    |      1 |
| gb2312   | GB2312 Simplified Chinese       | gb2312_chinese_ci   |      2 |
| greek    | ISO 8859-7 Greek                | greek_general_ci    |      1 |
| cp1250   | Windows Central European        | cp1250_general_ci   |      1 |
| gbk      | GBK Simplified Chinese          | gbk_chinese_ci      |      2 |
| latin5   | ISO 8859-9 Turkish              | latin5_turkish_ci   |      1 |
| armscii8 | ARMSCII-8 Armenian              | armscii8_general_ci |      1 |
| utf8     | UTF-8 Unicode                   | utf8_general_ci     |      3 |
| ucs2     | UCS-2 Unicode                   | ucs2_general_ci     |      2 |
| cp866    | DOS Russian                     | cp866_general_ci    |      1 |
| keybcs2  | DOS Kamenicky Czech-Slovak      | keybcs2_general_ci  |      1 |
| macce    | Mac Central European            | macce_general_ci    |      1 |
| macroman | Mac West European               | macroman_general_ci |      1 |
| cp852    | DOS Central European            | cp852_general_ci    |      1 |
| latin7   | ISO 8859-13 Baltic              | latin7_general_ci   |      1 |
| utf8mb4  | UTF-8 Unicode                   | utf8mb4_general_ci  |      4 |
| cp1251   | Windows Cyrillic                | cp1251_general_ci   |      1 |
| utf16    | UTF-16 Unicode                  | utf16_general_ci    |      4 |
| utf16le  | UTF-16LE Unicode                | utf16le_general_ci  |      4 |
| cp1256   | Windows Arabic                  | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic                  | cp1257_general_ci   |      1 |
| utf32    | UTF-32 Unicode                  | utf32_general_ci    |      4 |
| binary   | Binary pseudo charset           | binary              |      1 |
| geostd8  | GEOSTD8 Georgian                | geostd8_general_ci  |      1 |
| cp932    | SJIS for Windows Japanese       | cp932_japanese_ci   |      2 |
| eucjpms  | UJIS for Windows Japanese       | eucjpms_japanese_ci |      3 |
| gb18030  | China National Standard GB18030 | gb18030_chinese_ci  |      4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.00 sec)
 
mysql> SHOW VARIABLES LIKE '%char%';   //查看客户端的字符编码
......

mysql> SELECT CHARSET(email) FROM tbtest;	//查看某表中某字段使用的字符编码

mysql> SHOW ENGINES;        		//查看当前数据库支持的所有存储引擎
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| dnP                |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> SHOW TABLES FROM dnP;   //不进入某数据库而列出其包含的所有表
+---------------+
| Tables_in_dnP |
+---------------+
| dunianpei     |
+---------------+
1 row in set (0.00 sec)


//查看表结构
//语法：DESC [db_name.]table_name;
mysql> DESC dnP.dunianpei;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(50)      | NO   |     | NULL    |       |
| name  | varchar(120) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

//查看某表的创建命令，可以看到创建表时设置的参数
//语法：SHOW CREATE TABLE table_name;

mysql> SHOW CREATE TABLE dnP.dunianpei;
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table     | Create Table                                                                                                                                               |
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dunianpei | CREATE TABLE `dunianpei` (
  `id` int(50) NOT NULL,
  `name` varchar(120) NOT NULL,
  `age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

//查看某表的状态
//语法：SHOW TABLE STATUS LIKE 'table_name'\G

mysql> use dnP;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> SHOW TABLE STATUS LIKE 'dunianpei'\G   //查看dunianpei表的状态
*************************** 1. row ***************************
           Name: dunianpei
         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: 2022-07-26 14:11:27
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

1.5 ALTER修改操作

//修改数据库属性
//语法：ALTER DATABASE 'DB_NAME' CHARACTER SET charset_name | COLLATE collation_name

//修改数据库字符集为utf8
mysql> ALTER DATABASE dnP CHARACTER SET utf8;
Query OK, 1 row affected (0.00 sec)

//修改表
//语法：ALTER TABLE  [option]

//给dunianpei表添加新的一列，先查看表结构
mysql> DESC dunianpei;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(50)      | NO   |     | NULL    |       |
| name  | varchar(120) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

//给dunianpei表添加一列'phone'
mysql> ALTER TABLE dunianpei ADD phone int(11);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

//查看表结构
mysql> DESC dunianpei;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(50)      | NO   |     | NULL    |       |
| name  | varchar(120) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| phone | int(11)      | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

//修改dunianpei表中'phone'列为'sex'
mysql> ALTER TABLE dunianpei CHANGE phone sex varchar(4);
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC dunianpei;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(50)      | NO   |     | NULL    |       |
| name  | varchar(120) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| sex   | varchar(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

//修改表名为Sia
mysql> ALTER TABLE dunianpei RENAME TO Sia;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW TABLES;
+---------------+
| Tables_in_dnP |
+---------------+
| Sia           |
+---------------+
1 row in set (0.00 sec)

//修改数据库字符编码
mysql> ALTER DATABASE dbtest CHARACTER SET utf8 COLLATE utf8_general_ci;

//修改表字符编码
mysql> ALTER TABLE tbtest CHARACTER SET utf8 COLLATE utf8_general_ci;

1.6 获取帮助

//获取命令使用帮助
//语法：HELP commond;
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

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }

create_definition: {
    col_name column_definition
  | {INDEX | KEY} [index_name] [index_type] (key_part,...)
......
......

2、DML操作

DML操作包括增(INSERT)、删(DELETE)、改(UPDATE)、查(SELECT)，均属针对表的操作。

2.1 INSERT语句

//DML操作之增操作insert
//语法：INSERT [INTO] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...

mysql> use dnP;
Database changed

//一次插入一条记录
mysql> INSERT INTO Sia (id,name,age) VALUE (1,'tom',20);
Query OK, 1 row affected (0.00 sec)

//一次插入多条记录
mysql> INSERT INTO Sia (id,name,age) VALUES (2,'jerry',23),(3,'zbh',25),(4,'sean',28),(5,'zhangshan',26),(6,'zhangshan',20),(7,'lisi',NULL);
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

2.2 SELECT语句

字段column表示法

表示符	代表什么？
*	所有字段
as	字段别名，如col1 AS alias1 当表名很长时用别名代替

条件判断语句WHERE

操作类型	常用操作符
操作符	>，<，>=，<=，=，!= BETWEEN column# AND column# LIKE：模糊匹配 RLIKE：基于正则表达式进行模式匹配 IS NOT NULL：非空 IS NULL：空
条件逻辑操作	AND OR NOT

ORDER BY：排序，默认为升序（ASC）

ORDER BY语句	意义
ORDER BY ‘column_name’	根据column_name进行升序排序
ORDER BY ‘column_name’ DESC	根据column_name进行降序排序
ORDER BY ’column_name’ LIMIT 2	根据column_name进行升序排序 并只取前2个结果
ORDER BY ‘column_name’ LIMIT 1,2	根据column_name进行升序排序 并且略过第1个结果取后面的2个结果

//DML操作之查操作select
//语法：SELECT column1,column2,... FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> use dnP;
Database changed

mysql> select * from Sia;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  1 | tom       |   20 | NULL |
|  2 | jerry     |   23 | NULL |
|  3 | zbh       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
|  7 | lisi      | NULL | NULL |
|  1 | tom       |   20 | NULL |
+----+-----------+------+------+
8 rows in set (0.00 sec)

mysql> SELECT name FROM Sia;
+-----------+
| name      |
+-----------+
| tom       |
| jerry     |
| zbh       |
| sean      |
| zhangshan |
| zhangshan |
| lisi      |
| tom       |
+-----------+
8 rows in set (0.00 sec)

mysql> SELECT * FROM Sia WHERE age >= 25;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  3 | dnp       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan |   26 | NULL |
+----+-----------+------+------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM zbhtable WHERE age >= 25 AND name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan     |   26 |
+----+-----------+------+
1 row in set (0.00 sec)

mysql> SELECT * FROM Sia WHERE age BETWEEN 23 and 28;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  2 | jerry       |   23 | NULL |
|  3 | dnp       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan     |   26 | NULL |
+----+-----------+------+------+
4 rows in set (0.00 sec)

mysql> select * from Sia where age is not null;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  1 | tom       |   20 | NULL |
|  2 | jerry       |   23 | NULL |
|  3 | dnp       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan     |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
|  1 | tom       |   20 | NULL |
+----+-----------+------+------+
7 rows in set (0.00 sec)

mysql> select * from Sia where age is null;
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  7 | lisi | NULL | NULL |
+----+------+------+------+
1 row in set (0.00 sec)

mysql> select * from Sia where name like '%z%';
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  3 | zbh       |   25 | NULL |
|  5 | zhangshan |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
+----+-----------+------+------+
3 rows in set (0.00 sec)

2.3 update语句

//DML操作之改操作update
//语法：UPDATE table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> select * from Sia;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  1 | tom       |   20 | NULL |
|  2 | jerry     |   23 | NULL |
|  3 | zbh       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
|  7 | lisi      | NULL | NULL |
|  1 | tom       |   20 | NULL |
+----+-----------+------+------+
8 rows in set (0.00 sec)

mysql> update Sia set age = 30 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from Sia where name = 'lisi';
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  7 | lisi |   30 | NULL |
+----+------+------+------+
1 row in set (0.00 sec)

2.4 delete语句

//DML操作之删操作delete
//语法：DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> select * from Sia;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  1 | tom       |   20 | NULL |
|  2 | jerry     |   23 | NULL |
|  3 | zbh       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
|  7 | lisi      |   30 | NULL |
|  1 | tom       |   20 | NULL |
+----+-----------+------+------+
8 rows in set (0.00 sec)

mysql> delete from Sia where id = 7;   //删除某条记录
Query OK, 1 row affected (0.00 sec)

mysql> select * from Sia;
+----+-----------+------+------+
| id | name      | age  | sex  |
+----+-----------+------+------+
|  1 | tom       |   20 | NULL |
|  2 | jerry     |   23 | NULL |
|  3 | zbh       |   25 | NULL |
|  4 | sean      |   28 | NULL |
|  5 | zhangshan |   26 | NULL |
|  6 | zhangshan |   20 | NULL |
|  1 | tom       |   20 | NULL |
+----+-----------+------+------+
7 rows in set (0.00 sec)

mysql> delete from Sia;   //删除整张表的内容
Query OK, 7 rows affected (0.00 sec)

mysql> select * from Sia;
Empty set (0.00 sec)

mysql> desc Sia;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(50)      | NO   |     | NULL    |       |
| name  | varchar(120) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| sex   | varchar(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

2.5 truncate语句

truncate与delete的区别：

语句类型	特点
delete	DELETE删除表内容时仅删除内容，但会保留表结构 DELETE语句每次删除一行，并在事务日志中为所删除的每行记录一项 可以通过回滚事务日志恢复数据 非常占用空间
truncate	删除表中所有数据，且无法恢复 表结构、约束和索引等保持不变，新添加的行计数值重置为初始值 执行速度比DELETE快，且使用的系统和事务日志资源少 通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放 对于有外键约束引用的表，不能使用TRUNCATE TABLE删除数据 不能用于加入了索引视图的表

//语法：TRUNCATE table_name;

mysql> select * from Sia;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  1 | tom       |   20 |
|  2 | jerry     |   23 |
|  3 | dnp       |   25 |
|  4 | sean      |   28 |
|  5 | zhangshan |   26 |
|  6 | zhangshan |   20 |
|  7 | lisi      | NULL |
+----+-----------+------+
7 rows in set (0.00 sec)

mysql> truncate Sia;
Query OK, 0 rows affected (0.01 sec)

mysql> select * from Sia;
Empty set (0.00 sec)

mysql> desc Sia;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

3 DCL操作

3.1 创建授权grant

权限类型(priv_type)

权限类型	代表什么？
ALL	所有权限
SELECT	读取内容的权限
INSERT	插入内容的权限
UPDATE	更新内容的权限
DELETE	删除内容的权限

指定要操作的对象db_name.table_name

表示方式	意义
.	所有库的所有表
db_name	指定库的所有表
db_name.table_name	指定库的指定表

WITH GRANT OPTION：被授权的用户可将自己的权限副本转赠给其他用户，说白点就是将自己的权限完全复制给另一个用户。不建议使用。

语法：
GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| dnP                |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

//授权tom用户在数据库本机上登录访问所有数据库
mysql> grant all on *.* to 'tom'@'localhost' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.01 sec)

//也可表示为：
grant all on *.* to 'tom'@'127.0.0.1' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权tom用户在192.168.48.150上远程登录访问dnP数据库
mysql> grant all on dnP.* to 'tom'@'192.168.48.150' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权tom用户在所有位置上远程登录访问dnP数据库
mysql> grant all on dnP.* to 'tom'@'%' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

授权后利用student（图形化数据库）进行连接

查看授权

//查看当前登录用户的授权信息
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        |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)

//查看指定用户tom的授权信息
mysql> show grants for tom;
+----------------------------------------------+
| Grants for tom@%                             |
+----------------------------------------------+
| GRANT USAGE ON *.* TO 'tom'@'%'              |
| GRANT ALL PRIVILEGES ON `dnP`.* TO 'tom'@'%' |
+----------------------------------------------+
2 rows in set (0.00 sec)

mysql> show grants for 'tom'@'localhost';
+--------------------------------------------------+
| Grants for tom@localhost                         |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'localhost' |
+--------------------------------------------------+
1 row in set (0.00 sec)

mysql> show grants for 'tom'@'127.0.0.1';
+--------------------------------------------------+
| Grants for [email protected]                         |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'tom'@'127.0.0.1' |
+--------------------------------------------------+
1 row in set (0.00 sec)

取消授权

//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';

mysql> show grants for 'tom'@'192.168.48.150';
+-----------------------------------------------------------+
| Grants for [email protected]                             |
+-----------------------------------------------------------+
| GRANT USAGE ON *.* TO 'tom'@'192.168.48.150'              |
| GRANT ALL PRIVILEGES ON `dnP`.* TO 'tom'@'192.168.48.150' |
+-----------------------------------------------------------+
2 rows in set (0.00 sec)

mysql> revoke all on dada.* from 'tom'@'192.168.48.150';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> show grants for 'tom'@'192.168.48.150';
+----------------------------------------------------------------+
| Grants for [email protected]                                 |
+----------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'tom'@'192.168.48.150'                  |
| GRANT ALL PRIVILEGES ON `dnP`.* TO 'tom'@'192.168.48.150' |
+----------------------------------------------------------------+
2 rows in set (0.00 sec)

实战案例

1.搭建mysql服务

[root@localhost ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# rpm -Uvh mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# yum  module disable mysql
[root@localhost ~]# yum -y install mysql-community-server mysql-community-client  mysql-community-common mysql-community-devel  --nogpgcheck
[root@localhost ~]# rpm -e mysql57-community-release
[root@localhost ~]# systemctl enable --now mysqld
[root@localhost ~]# grep "password" /var/log/mysqld.log
[root@localhost ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.39

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)

mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)

mysql> set password = password('123456');
[root@localhost ~]# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 5.7.39 MySQL Community Server (GPL)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

2.创建一个以你名字为名的数据库，并创建一张表student，该表包含三个字段（id，name，age），表结构如下：

mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(100) | NO   |     | NULL    |                |
| age   | tinyint(4)   | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)
mysql> create database if not exists dnP;
Query OK, 1 row affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| dnP            |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> use dnP;
Database changed

mysql> create table student (id int(11) not null key auto_increment,name varchar(100) not null,age tinyint(4));
Query OK, 0 rows affected (0.00 sec)

mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(100) | NO   |     | NULL    |                |
| age   | tinyint(4)   | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

3.查看下该新建的表有无内容（用select语句）

mysql> select * from student;
Empty set (0.00 sec)

4.往新建的student表中插入数据（用insert语句），结果应如下所示：

+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | dnP    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
|  7 | lisi        | NULL |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
mysql> insert into student (id,name,age) value (1,'tom',20);
Query OK, 1 row affected (0.00 sec)

mysql> insert into student (id,name,age) values (2,'jerry',23),(3,'dnP',25),(4,'sean',28),(5,'zhangshan',26),(6,'zhangshan',20),(7,'lisi',null),(8,'chenshuo',10),(9,'wangwu',3),(10,'qiuyi',15),(11,'qiuxiaotian',20);
Query OK, 10 rows affected (0.00 sec)
Records: 10  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | dnP    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
|  7 | lisi        | NULL |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
11 rows in set (0.00 sec)

5.修改lisi的年龄为50

mysql> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student where name = 'lisi';
+----+------+------+
| id | name | age  |
+----+------+------+
|  7 | lisi |   50 |
+----+------+------+
1 row in set (0.00 sec)

6.以age字段降序排序

mysql> select * from student order by age desc;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  7 | lisi        |   50 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  3 | dnP    |   25 |
|  2 | jerry       |   23 |
|  1 | tom         |   20 |
|  6 | zhangshan   |   20 |
| 11 | qiuxiaotian |   20 |
| 10 | qiuyi       |   15 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
+----+-------------+------+
11 rows in set (0.00 sec)

7.查询student表中年龄最小的3位同学跳过前2位

mysql> select * from student order by age limit 2,3;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
| 10 | qiuyi       |   15 |
|  1 | tom         |   20 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
3 rows in set (0.00 sec)

8.查询student表中年龄最大的4位同学

mysql> select * from student order by age desc limit 4;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  7 | lisi      |   50 |
|  4 | sean      |   28 |
|  5 | zhangshan |   26 |
|  3 | dnP  |   25 |
+----+-----------+------+
4 rows in set (0.00 sec)

9.查询student表中名字叫zhangshan的记录

mysql> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
|  6 | zhangshan |   20 |
+----+-----------+------+
2 rows in set (0.00 sec)

10.查询student表中名字叫zhangshan且年龄大于20岁的记录

mysql> select * from student where age > 20 and name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
+----+-----------+------+
1 row in set (0.00 sec)

11.查询student表中年龄在23到30之间的记录

mysql> select * from student where age > 23 and age < 30;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  3 | dnP  |   25 |
|  4 | sean      |   28 |
|  5 | zhangshan |   26 |
+----+-----------+------+
3 rows in set (0.00 sec)

12.修改wangwu的年龄为100

mysql> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student where name = 'wangwu';
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  9 | wangwu |  100 |
+----+--------+------+
1 row in set (0.00 sec)

13.删除student中名字叫zhangshan且年龄小于等于20的记录

mysql> delete from student where name = 'zhangshan';
Query OK, 2 rows affected (0.00 sec)

mysql> delete from student where age <= 20;
Query OK, 4 rows affected (0.00 sec)

mysql> select * from student;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | dnP |   25 |
|  4 | sean     |   28 |
|  7 | lisi     |   50 |
|  9 | wangwu   |  100 |
+----+----------+------+
5 rows in set (0.00 sec)