mysql进阶

2022/7/29 2:54:40

本文主要是介绍mysql进阶,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!

mysql进阶

目录
  • 1. 二进制格式mysql安装
  • 2. mysql配置文件
    • 2.1 数据库密码破解:
  • 3. 多表联合查询
    • 3.1 什么是多表联合查询
    • 3.2 交叉连接(CROSS JOIN)
      • 3.2.1 笛卡尔积
      • 3.2.2 交叉连接

1. 二进制格式mysql安装

  • 1.下载二进制格式的mysql软件包
[root@mr ~]# wget https://downloads.mysql.com/archives/get/p/23/file/mysql-5.7.38-linux-glibc2.12-x86_64.tar.gz
[root@mr ~]# cd /usr/src/
[root@mr src]# ls
debug  kernels  mysql-5.7.38-linux-glibc2.12-x86_64.tar.gz
[root@mr src]# 

  • 2.创建用户和组,解压软件至/usr/local/,修改目录/usr/local/mysql的属主属组
[root@mr src]# id mysql
id: ‘mysql’: no such user
[root@mr src]# useradd -M -r -s /sbin/nologin mysql
[root@mr src]# id mysql
uid=993(mysql) gid=990(mysql) groups=990(mysql)
[root@mr src]# tar xf mysql-5.7.38-linux-glibc2.12-x86_64.tar.gz -C /usr/local/
[root@mr src]# cd /usr/local/
[root@mr local]# ll
total 0
drwxr-xr-x. 2 root root  18 Jul  7 10:28 bin
drwxr-xr-x. 2 root root   6 May 19  2020 etc
drwxr-xr-x. 2 root root   6 May 19  2020 games
drwxr-xr-x. 2 root root   6 May 19  2020 include
drwxr-xr-x. 2 root root   6 May 19  2020 lib
drwxr-xr-x. 3 root root  17 Jul  1 09:26 lib64
drwxr-xr-x. 2 root root   6 May 19  2020 libexec
drwxr-xr-x. 9 root root 129 Jul 27 16:03 mysql-5.7.38-linux-glibc2.12-x86_64
drwxr-xr-x. 2 root root   6 May 19  2020 sbin
drwxr-xr-x. 6 root root  64 Jul  7 10:28 share
drwxr-xr-x. 2 root root   6 May 19  2020 src
[root@mr local]# ln -sv mysql-5.7.38-linux-glibc2.12-x86_64 mysql
'mysql' -> 'mysql-5.7.38-linux-glibc2.12-x86_64'
[root@mr local]# ll
total 0
drwxr-xr-x. 2 root root  18 Jul  7 10:28 bin
drwxr-xr-x. 2 root root   6 May 19  2020 etc
drwxr-xr-x. 2 root root   6 May 19  2020 games
drwxr-xr-x. 2 root root   6 May 19  2020 include
drwxr-xr-x. 2 root root   6 May 19  2020 lib
drwxr-xr-x. 3 root root  17 Jul  1 09:26 lib64
drwxr-xr-x. 2 root root   6 May 19  2020 libexec
lrwxrwxrwx. 1 root root  35 Jul 27 16:04 mysql -> mysql-5.7.38-linux-glibc2.12-x86_64
drwxr-xr-x. 9 root root 129 Jul 27 16:03 mysql-5.7.38-linux-glibc2.12-x86_64
drwxr-xr-x. 2 root root   6 May 19  2020 sbin
drwxr-xr-x. 6 root root  64 Jul  7 10:28 share
drwxr-xr-x. 2 root root   6 May 19  2020 src
[root@mr local]# 
[root@mr local]# chown -R mysql.mysql mysql*
[root@mr local]# ll
total 0
drwxr-xr-x. 2 root  root   18 Jul  7 10:28 bin
drwxr-xr-x. 2 root  root    6 May 19  2020 etc
drwxr-xr-x. 2 root  root    6 May 19  2020 games
drwxr-xr-x. 2 root  root    6 May 19  2020 include
drwxr-xr-x. 2 root  root    6 May 19  2020 lib
drwxr-xr-x. 3 root  root   17 Jul  1 09:26 lib64
drwxr-xr-x. 2 root  root    6 May 19  2020 libexec
lrwxrwxrwx. 1 mysql mysql  35 Jul 27 16:04 mysql -> mysql-5.7.38-linux-glibc2.12-x86_64
drwxr-xr-x. 9 mysql mysql 129 Jul 27 16:03 mysql-5.7.38-linux-glibc2.12-x86_64
drwxr-xr-x. 2 root  root    6 May 19  2020 sbin
drwxr-xr-x. 6 root  root   64 Jul  7 10:28 share
drwxr-xr-x. 2 root  root    6 May 19  2020 src
[root@mr local]# 

    1. 添加环境变量
[root@mr ~]# cd /usr/local/mysql
[root@mr mysql]# ls
bin  docs  include  lib  LICENSE  man  README  share  support-files
[root@mr mysql]# cd bin/
[root@mr bin]# pwd
/usr/local/mysql/bin
[root@mr bin]# echo 'export PATH=$PATH:/usr/local/mysql/bin' > /etc/profile.d/mysql.sh
[root@mr bin]# source /etc/profile.d/mysql.sh 
[root@mr bin]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/usr/local/mysql/bin
[root@mr bin]# which mysql
/usr/local/mysql/bin/mysql
[root@mr bin]# 
[root@mr mysql]# ln -sv /usr/local/mysql/include/ /usr/include/mysql
'/usr/include/mysql' -> '/usr/local/mysql/include/'
[root@mr mysql]# vim /etc/ld.so.conf.d/mysql.conf

/usr/local/mysql/lib/
[root@mr mysql]# ldconfig
[root@mr mysql]# vim /etc/man_db.conf
MANDATORY_MANPATH                       /usr/man
MANDATORY_MANPATH                       /usr/share/man
MANDATORY_MANPATH                       /usr/local/share/man
MANDATORY_MANPATH                       /usr/local/mysql/man

    1. 建立数据存放目录,初始化数据库
[root@mr ~]# mkdir /opt/data
[root@mr ~]# ll /opt/data/
total 0
[root@mr ~]# chown -R mysql.mysql /opt/data/
[root@mr ~]# mysql --initialize --user mysql --datadir /opt/data/
mysql: error while loading shared libraries: libncurses.so.5: cannot open shared object file: No such file or directory
[root@mr ~]# mysqld --initialize --user mysql --datadir /opt/data/
2022-07-27T08:21:49.390169Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2022-07-27T08:21:49.520539Z 0 [Warning] InnoDB: New log files created, LSN=45790
2022-07-27T08:21:49.548430Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2022-07-27T08:21:49.557890Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: 29732c94-0d85-11ed-925a-000c29e8e4aa.
2022-07-27T08:21:49.558494Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2022-07-27T08:21:50.271098Z 0 [Warning] A deprecated TLS version TLSv1 is enabled. Please use TLSv1.2 or higher.
2022-07-27T08:21:50.271141Z 0 [Warning] A deprecated TLS version TLSv1.1 is enabled. Please use TLSv1.2 or higher.
2022-07-27T08:21:50.271798Z 0 [Warning] CA certificate ca.pem is self signed.
2022-07-27T08:21:50.425296Z 1 [Note] A temporary password is generated for root@localhost: -ff3uq#Fee%k
[root@mr ~]# 
[root@mr ~]# echo '-ff3uq#Fee%k' > pass
[root@mr ~]# cat pass
-ff3uq#Fee%k

    1. 生成配置文件
[root@mr ~]# vim /etc/my.cnf
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
socket = /tmp/mysql.sock
port = 3306
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve
sql-mode = STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

    1. 配置服务启动脚本,启动mysql
[root@mr mysql]# cd support-files/
[root@mr support-files]# ls
magic  mysqld_multi.server  mysql-log-rotate  mysql.server
[root@mr support-files]# file mysql.server 
mysql.server: POSIX shell script, ASCII text executable
[root@mr support-files]# 
方法一:
[root@mr ~]# /usr/local/mysql/support-files/mysql.server start
Starting MySQL.Logging to '/opt/data/mr.err'.
 SUCCESS! 
[root@mr ~]# ss -antl
State    Recv-Q   Send-Q     Local Address:Port      Peer Address:Port   Process   
LISTEN   0        128              0.0.0.0:111            0.0.0.0:*                
LISTEN   0        128              0.0.0.0:22             0.0.0.0:*                
LISTEN   0        25               0.0.0.0:514            0.0.0.0:*                
LISTEN   0        80                     *:3306                 *:*                
LISTEN   0        128                 [::]:111               [::]:*                
LISTEN   0        128                 [::]:22                [::]:*                
LISTEN   0        25                  [::]:514               [::]:*                
[root@mr ~]# /usr/local/mysql/support-files/mysql.server stop
Shutting down MySQL.. SUCCESS! 
[root@mr ~]# ss -antl
State    Recv-Q   Send-Q     Local Address:Port      Peer Address:Port   Process   
LISTEN   0        128              0.0.0.0:111            0.0.0.0:*                
LISTEN   0        128              0.0.0.0:22             0.0.0.0:*                
LISTEN   0        25               0.0.0.0:514            0.0.0.0:*                
LISTEN   0        128                 [::]:111               [::]:*                
LISTEN   0        128                 [::]:22                [::]:*                
LISTEN   0        25                  [::]:514               [::]:*                
方法二:
[root@mr ~]# cp -a /usr/local/mysql/support-files/mysql.server /etc/init.d/mysqld
[root@mr ~]# vim /etc/init.d/mysqld 
basedir=/usr/local/mysql/
datadir=/opt/data/
[root@mr ~]# service mysqld start
Starting MySQL. SUCCESS! 
[root@mr ~]# service mysqld stop
Shutting down MySQL.. SUCCESS! 
[root@mr ~]# ss -antl
State    Recv-Q   Send-Q     Local Address:Port      Peer Address:Port   Process   
LISTEN   0        128              0.0.0.0:111            0.0.0.0:*                
LISTEN   0        128              0.0.0.0:22             0.0.0.0:*                
LISTEN   0        25               0.0.0.0:514            0.0.0.0:*                
LISTEN   0        128                 [::]:111               [::]:*                
LISTEN   0        128                 [::]:22                [::]:*                
LISTEN   0        25                  [::]:514               [::]:*                
[root@mr ~]# rm -rf /etc/init.d/mysqld 
[root@mr ~]# service mysqld start
Redirecting to /bin/systemctl start mysqld.service
Failed to start mysqld.service: Unit mysqld.service not found.
[root@mr ~]# service mysqld stop
Redirecting to /bin/systemctl stop mysqld.service
Failed to stop mysqld.service: Unit mysqld.service not loaded.
[root@mr ~]# ss -antl
State    Recv-Q   Send-Q     Local Address:Port      Peer Address:Port   Process   
LISTEN   0        128              0.0.0.0:111            0.0.0.0:*                
LISTEN   0        128              0.0.0.0:22             0.0.0.0:*                
LISTEN   0        25               0.0.0.0:514            0.0.0.0:*                
LISTEN   0        128                 [::]:111               [::]:*                
LISTEN   0        128                 [::]:22                [::]:*                
LISTEN   0        25                  [::]:514               [::]:*                
[root@mr ~]# 

[root@mr ~]# cp /usr/lib/systemd/system/sshd.service .
[root@mr ~]# ls
 sshd.service
[root@mr ~]# mv sshd.service mysqld.service
[root@mr ~]# ls
mysqld.service
[root@mr ~]#vim mysqld.service
[Unit]
Description=mysql server daemon
After=network.target sshd-keygen.target

[Service]
Type=forking
ExecStart=/usr/local/mysql/support-files/mysql.server start
ExecStop=/usr/local/mysql/support-files/mysql.server stop
ExecReload=/bin/kill -HUP $MAINPID

[Install]
WantedBy=multi-user.target
[root@mr ~]# systemctl daemon-reload
[root@mr ~]# systemctl stop firewalld
[root@mr ~]# systemctl disable firewalld
Removed /etc/systemd/system/multi-user.target.wants/firewalld.service.
Removed /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.
[root@mr ~]# vim /etc/selinux/config
SELINUX=disabled
[root@mr ~]# setenforce 0
[root@mr ~]# systemctl start mysqld
[root@mr ~]# ss -antl
State    Recv-Q   Send-Q     Local Address:Port      Peer Address:Port   Process   
LISTEN   0        128              0.0.0.0:111            0.0.0.0:*                
LISTEN   0        128              0.0.0.0:22             0.0.0.0:*                
LISTEN   0        25               0.0.0.0:514            0.0.0.0:*                
LISTEN   0        80                     *:3306                 *:*                
LISTEN   0        128                 [::]:111               [::]:*                
LISTEN   0        128                 [::]:22                [::]:*                
LISTEN   0        25                  [::]:514               [::]:*                
[root@mr ~]# 


  • 7.修改密码,使用临时密码登录
[root@mr ~]# mysql -uroot -p'-ff3uq#Fee%k'
mysql: error while loading shared libraries: libncurses.so.5: cannot open shared object file: No such file or directory
[root@mr ~]# yum whatprovides libncurses.so.5
Last metadata expiration check: 0:34:58 ago on Wed 27 Jul 2022 05:02:10 PM CST.
ncurses-compat-libs-6.1-7.20180224.el8.i686 : Ncurses compatibility libraries
Repo        : baseos
Matched from:
Provide    : libncurses.so.5

ncurses-compat-libs-6.1-9.20180224.el8.i686 : Ncurses compatibility libraries
Repo        : baseos
Matched from:
Provide    : libncurses.so.5

[root@mr ~]# dnf install -y ncurses-compat-libs
Last metadata expiration check: 0:35:39 ago on Wed 27 Jul 2022 05:02:10 PM CST.
Dependencies resolved.
===================================================================================
 Package                  Arch        Version                    Repository   Size
===================================================================================
Installing:
 ncurses-compat-libs      x86_64      6.1-9.20180224.el8         baseos      328 k

Transaction Summary
===================================================================================
Install  1 Package

Total download size: 328 k
Installed size: 1.0 M
Downloading Packages:
ncurses-compat-libs-6.1-9.20180224.el8.x86_64.rpm  735 kB/s | 328 kB     00:00    
-----------------------------------------------------------------------------------
Total                                              378 kB/s | 328 kB     00:00     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                           1/1 
  Installing       : ncurses-compat-libs-6.1-9.20180224.el8.x86_64             1/1 
  Running scriptlet: ncurses-compat-libs-6.1-9.20180224.el8.x86_64             1/1 
  Verifying        : ncurses-compat-libs-6.1-9.20180224.el8.x86_64             1/1 
Installed products updated.

Installed:
  ncurses-compat-libs-6.1-9.20180224.el8.x86_64                                    

Complete!
[root@mr ~]#  mysql -uroot -p'-ff3uq#Fee%k'
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 2
Server version: 5.7.38

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 password = password('123456');
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> exit
Bye
[root@mr ~]# 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 3
Server version: 5.7.38 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> 


2. mysql配置文件

mysql的配置文件为/etc/my.cnf

配置文件查找次序:若在多个配置文件中均有设定,则最后找到的最终生效

[root@mr ~]# vim .my.cnf
[client]
user=root
password=123456
[root@mr ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.38 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> 

mysql常用配置文件参数

参数 说明
port = 3306 设置监听端口
socket = /tmp/mysql.sock 指定套接字文件位置
basedir = /usr/local/mysql 指定MySQL的安装路径
datadir = /data/mysql 指定MySQL的数据存放路径
pid-file = /data/mysql/mysql.pid 指定进程ID文件存放路径
user = mysql 指定MySQL以什么用户的身份提供服务
skip-name-resolve 禁止MySQL对外部连接进行DNS解析,使用这一选项可以消除MySQL进行DNS解析的时间。若开启该选项,则所有远程主机连接授权都要使用IP地址方式否则MySQL将无法正常处理连接请求
[root@mr ~]# ps -ef | grep mysqld
root       11805       1  0 17:33 ?        00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/opt/data --pid-file=/opt/data/mysql.pid
mysql      12007   11805  0 17:33 ?        00:00:00 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/opt/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=mr.err --pid-file=/opt/data/mysql.pid --socket=/tmp/mysql.sock --port=3306
root       12067    8399  0 17:53 pts/0    00:00:00 grep --color=auto mysqld
[root@mr ~]# 

2.1 数据库密码破解:

[root@mr ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.38 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> exit
Bye
[root@mr ~]# 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 7
Server version: 5.7.38 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> exit
Bye
[root@mr ~]# rm -rf .my.cnf 
[root@mr ~]# mysql
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@mr ~]# vim /etc/my.cnf
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
socket = /tmp/mysql.sock
port = 3306
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve
skip-grant-tables
sql-mode = STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
[root@mr ~]# systemctl restart mysqld
[root@mr ~]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.38 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> 
mysql> set password = password('marui');
ERROR 1290 (HY000): The MySQL server is running with the --skip-grant-tables option so it cannot execute this statement
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (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

Database changed

mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| engine_cost               |
| event                     |
| func                      |
| general_log               |
| gtid_executed             |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| innodb_index_stats        |
| innodb_table_stats        |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| server_cost               |
| servers                   |
| slave_master_info         |
| slave_relay_log_info      |
| slave_worker_info         |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
31 rows in set (0.01 sec)

mysql> desc user;
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Field                  | Type                              | Null | Key | Default               | Extra |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Host                   | char(60)                          | NO   | PRI |                       |       |
| User                   | char(32)                          | NO   | PRI |                       |       |
| Select_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Insert_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Update_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Delete_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Create_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Drop_priv              | enum('N','Y')                     | NO   |     | N                     |       |
| Reload_priv            | enum('N','Y')                     | NO   |     | N                     |       |
| Shutdown_priv          | enum('N','Y')                     | NO   |     | N                     |       |
| Process_priv           | enum('N','Y')                     | NO   |     | N                     |       |
| File_priv              | enum('N','Y')                     | NO   |     | N                     |       |
| Grant_priv             | enum('N','Y')                     | NO   |     | N                     |       |
| References_priv        | enum('N','Y')                     | NO   |     | N                     |       |
| Index_priv             | enum('N','Y')                     | NO   |     | N                     |       |
| Alter_priv             | enum('N','Y')                     | NO   |     | N                     |       |
| Show_db_priv           | enum('N','Y')                     | NO   |     | N                     |       |
| Super_priv             | enum('N','Y')                     | NO   |     | N                     |       |
| Create_tmp_table_priv  | enum('N','Y')                     | NO   |     | N                     |       |
| Lock_tables_priv       | enum('N','Y')                     | NO   |     | N                     |       |
| Execute_priv           | enum('N','Y')                     | NO   |     | N                     |       |
| Repl_slave_priv        | enum('N','Y')                     | NO   |     | N                     |       |
| Repl_client_priv       | enum('N','Y')                     | NO   |     | N                     |       |
| Create_view_priv       | enum('N','Y')                     | NO   |     | N                     |       |
| Show_view_priv         | enum('N','Y')                     | NO   |     | N                     |       |
| Create_routine_priv    | enum('N','Y')                     | NO   |     | N                     |       |
| Alter_routine_priv     | enum('N','Y')                     | NO   |     | N                     |       |
| Create_user_priv       | enum('N','Y')                     | NO   |     | N                     |       |
| Event_priv             | enum('N','Y')                     | NO   |     | N                     |       |
| Trigger_priv           | enum('N','Y')                     | NO   |     | N                     |       |
| Create_tablespace_priv | enum('N','Y')                     | NO   |     | N                     |       |
| ssl_type               | enum('','ANY','X509','SPECIFIED') | NO   |     |                       |       |
| ssl_cipher             | blob                              | NO   |     | NULL                  |       |
| x509_issuer            | blob                              | NO   |     | NULL                  |       |
| x509_subject           | blob                              | NO   |     | NULL                  |       |
| max_questions          | int(11) unsigned                  | NO   |     | 0                     |       |
| max_updates            | int(11) unsigned                  | NO   |     | 0                     |       |
| max_connections        | int(11) unsigned                  | NO   |     | 0                     |       |
| max_user_connections   | int(11) unsigned                  | NO   |     | 0                     |       |
| plugin                 | char(64)                          | NO   |     | mysql_native_password |       |
| authentication_string  | text                              | YES  |     | NULL                  |       |
| password_expired       | enum('N','Y')                     | NO   |     | N                     |       |
| password_last_changed  | timestamp                         | YES  |     | NULL                  |       |
| password_lifetime      | smallint(5) unsigned              | YES  |     | NULL                  |       |
| account_locked         | enum('N','Y')                     | NO   |     | N                     |       |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
45 rows in set (0.00 sec)

mysql> 
mysql> select * from user\G
*************************** 1. row ***************************
                  Host: localhost
                  User: root
           Select_priv: Y
         ........
            Alter_priv: Y
          Show_db_priv: Y
            Super_priv: Y
 Create_tmp_table_priv: Y
      Lock_tables_priv: Y
          Execute_priv: Y
       Repl_slave_priv: Y
      Repl_client_priv: Y
      Create_view_priv: Y
        Show_view_priv: Y
   Create_routine_priv: Y
    Alter_routine_priv: Y
      Create_user_priv: Y
            Event_priv: Y
          Trigger_priv: Y
Create_tablespace_priv: Y
              ssl_type: 
            ssl_cipher: 
           x509_issuer: 
          x509_subject: 
         max_questions: 0
           max_updates: 0
       max_connections: 0
  max_user_connections: 0
                plugin: mysql_native_password
 authentication_string: *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9
      password_expired: N
 password_last_changed: 2022-07-27 17:39:05
     password_lifetime: NULL
        account_locked: N
*************************** 2. row ***************************
                  Host: localhost
......
mysql> update user set  authentication_string =password('marui') where User = 'root' and Host = 'localhost';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

mysql> select * from user\G
*************************** 1. row ***************************
                  Host: localhost
                  User: root
           Select_priv: Y
           Insert_priv: Y
           Update_priv: Y
           Delete_priv: Y
    ......
    
         max_questions: 0
           max_updates: 0
       max_connections: 0
  max_user_connections: 0
                plugin: mysql_native_password
 authentication_string: *9370E4584BA357054A156F3EF8CBCE33FBAB4BF3
      password_expired: N
 password_last_changed: 2022-07-27 17:39:05
     password_lifetime: NULL
......
mysql> exit
Bye
[root@mr ~]# vim /etc/my.cnf 
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
socket = /tmp/mysql.sock
port = 3306
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve
sql-mode = STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
[root@mr ~]# systemctl restart mysqld
[root@mr ~]# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root@mr ~]# mysql -uroot -pmarui
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 3
Server version: 5.7.38 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> 

3. 多表联合查询

3.1 什么是多表联合查询

前面所讲的查询语句都是针对一个表的,但是在关系型数据库中,表与表之间是有联系的,所以在实际应用中,经常使用多表查询。多表查询就是同时查询两个或两个以上的表。

在 MySQL 中,多表查询主要有交叉连接、内连接、外连接、分组查询与子查询等5种。

3.2 交叉连接(CROSS JOIN)

3.2.1 笛卡尔积

交叉连接(CROSS JOIN):有两种,显式的和隐式的2种,一般用来返回连接表的笛卡尔积。
笛卡尔积(Cartesian product)是指两个集合 X 和 Y 的乘积。

多表查询遵循的算法就是以上提到的笛卡尔积,表与表之间的连接可以看成是在做乘法运算。在实际应用中,应避免使用笛卡尔积,因为笛卡尔积中容易存在大量的不合理数据,简单来说就是容易导致查询结果重复、混乱。

3.2.2 交叉连接

交叉连接的语法格式如下:
SELECT <字段名> FROM <表1> CROSS JOIN <表2> [WHERE子句];

SELECT <字段名> FROM <表1>, <表2> [WHERE子句];
语法说明如下:

  • 字段名:需要查询的字段名称。
  • <表1><表2>:需要交叉连接的表名。
  • WHERE 子句:用来设置交叉连接的查询条件。

注意:多个表交叉连接时,在 FROM 后连续使用 CROSS JOIN 或,即可。以上两种语法的返回结果是相同的,但是第一种语法才是官方建议的标准写法。

当连接的表之间没有关系时,我们会省略掉 WHERE 子句,这时返回结果就是两个表的笛卡尔积,返回结果数量就是两个表的数据行相乘。需要注意的是,如果每个表有 1000 行,那么返回结果的数量就有 1000×1000 = 1000000 行,数据量是非常巨大的。

交叉连接可以查询两个或两个以上的表,为了更好的理解,我们就讲解两个表的交叉连接查询。
例 1
查询学生信息表和科目信息表,并得到一个笛卡尔积。

为了方便观察学生信息表和科目表交叉连接后的运行结果,我们先分别查询出这两个表的数据,再进行交叉连接查询。
1)查询 tb_students_info 表中的数据,SQL 语句和运行结果如下:

mysql> create database runtime;
Query OK, 1 row affected (0.00 sec)

mysql> use runtime;
Database changed
mysql> create table tb_students_info(id int not null primary key auto_increment,name varchar(50),age tinyint,sex varchar(4),height float,course_id int);
Query OK, 0 rows affected (0.00 sec)

mysql> desc tb_students_info;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| id        | int(11)     | NO   | PRI | NULL    | auto_increment |
| name      | varchar(50) | YES  |     | NULL    |                |
| age       | tinyint(4)  | YES  |     | NULL    |                |
| sex       | varchar(4)  | YES  |     | NULL    |                |
| height    | float       | YES  |     | NULL    |                |
| course_id | int(11)     | YES  |     | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+
6 rows in set (0.01 sec)

mysql> insert tb_students_info (name,age,sex,height,course_id) values('Dany',25,'W',160,1),('Green',23,'W',158,2),('Henry',23,'M',185,1),('Jane',22,'W',62,3),('Jim',24,'M',175,2),('John',21,'M',172,4),('Lily',22,'W',165,4),('Susan',23,'W',170,5),('Thomas',22,'M',178,5),('Tom',23,'M',165,5);
Query OK, 10 rows affected (0.00 sec)
Records: 10  Duplicates: 0  Warnings: 0

mysql> select * from tb_students_info;
+----+--------+------+------+--------+-----------+
| id | name   | age  | sex  | height | course_id |
+----+--------+------+------+--------+-----------+
|  1 | Dany   |   25 | W    |    160 |         1 |
|  2 | Green  |   23 | W    |    158 |         2 |
|  3 | Henry  |   23 | M    |    185 |         1 |
|  4 | Jane   |   22 | W    |     62 |         3 |
|  5 | Jim    |   24 | M    |    175 |         2 |
|  6 | John   |   21 | M    |    172 |         4 |
|  7 | Lily   |   22 | W    |    165 |         4 |
|  8 | Susan  |   23 | W    |    170 |         5 |
|  9 | Thomas |   22 | M    |    178 |         5 |
| 10 | Tom    |   23 | M    |    165 |         5 |
+----+--------+------+------+--------+-----------+
10 rows in set (0.00 sec)

mysql> show tables;
+-------------------+
| Tables_in_runtime |
+-------------------+
| tb_students_info  |
+-------------------+
1 row in set (0.00 sec)

mysql> create table tb_course(id int not null primary key auto_increment,course_name varchar(50));
Query OK, 0 rows affected (0.01 sec)

mysql> desc tb_course;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     | NO   | PRI | NULL    | auto_increment |
| course_name | varchar(50) | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> insert tb_course(course_name) values('Java'),('Mysql'),('Python'),('Go'),('C++');
Query OK, 5 rows affected (0.01 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> select * from tb_course;
+----+-------------+
| id | course_name |
+----+-------------+
|  1 | Java        |
|  2 | Mysql       |
|  3 | Python      |
|  4 | Go          |
|  5 | C++         |
+----+-------------+
5 rows in set (0.00 sec)

mysql> mysql> show tables;
+-------------------+
| Tables_in_runtime |
+-------------------+
| tb_course         |
| tb_students_info  |
+-------------------+
2 rows in set (0.00 sec)

mysql> select * from tb_students_info cross join tb_course;
+----+--------+------+------+--------+-----------+----+-------------+
| id | name   | age  | sex  | height | course_id | id | course_name |
+----+--------+------+------+--------+-----------+----+-------------+
|  1 | Dany   |   25 | W    |    160 |         1 |  1 | Java        |
|  1 | Dany   |   25 | W    |    160 |         1 |  2 | Mysql       |
|  1 | Dany   |   25 | W    |    160 |         1 |  3 | Python      |
|  1 | Dany   |   25 | W    |    160 |         1 |  4 | Go          |
|  1 | Dany   |   25 | W    |    160 |         1 |  5 | C++         |
|  2 | Green  |   23 | W    |    158 |         2 |  1 | Java        |
|  2 | Green  |   23 | W    |    158 |         2 |  2 | Mysql       |
|  2 | Green  |   23 | W    |    158 |         2 |  3 | Python      |
|  2 | Green  |   23 | W    |    158 |         2 |  4 | Go          |
|  2 | Green  |   23 | W    |    158 |         2 |  5 | C++         |
|  3 | Henry  |   23 | M    |    185 |         1 |  1 | Java        |
|  3 | Henry  |   23 | M    |    185 |         1 |  2 | Mysql       |
|  3 | Henry  |   23 | M    |    185 |         1 |  3 | Python      |
|  3 | Henry  |   23 | M    |    185 |         1 |  4 | Go          |
|  3 | Henry  |   23 | M    |    185 |         1 |  5 | C++         |
|  4 | Jane   |   22 | W    |     62 |         3 |  1 | Java        |
|  4 | Jane   |   22 | W    |     62 |         3 |  2 | Mysql       |
|  4 | Jane   |   22 | W    |     62 |         3 |  3 | Python      |
|  4 | Jane   |   22 | W    |     62 |         3 |  4 | Go          |
|  4 | Jane   |   22 | W    |     62 |         3 |  5 | C++         |
|  5 | Jim    |   24 | M    |    175 |         2 |  1 | Java        |
|  5 | Jim    |   24 | M    |    175 |         2 |  2 | Mysql       |
|  5 | Jim    |   24 | M    |    175 |         2 |  3 | Python      |
|  5 | Jim    |   24 | M    |    175 |         2 |  4 | Go          |
|  5 | Jim    |   24 | M    |    175 |         2 |  5 | C++         |
|  6 | John   |   21 | M    |    172 |         4 |  1 | Java        |
|  6 | John   |   21 | M    |    172 |         4 |  2 | Mysql       |
|  6 | John   |   21 | M    |    172 |         4 |  3 | Python      |
|  6 | John   |   21 | M    |    172 |         4 |  4 | Go          |
|  6 | John   |   21 | M    |    172 |         4 |  5 | C++         |
|  7 | Lily   |   22 | W    |    165 |         4 |  1 | Java        |
|  7 | Lily   |   22 | W    |    165 |         4 |  2 | Mysql       |
|  7 | Lily   |   22 | W    |    165 |         4 |  3 | Python      |
|  7 | Lily   |   22 | W    |    165 |         4 |  4 | Go          |
|  7 | Lily   |   22 | W    |    165 |         4 |  5 | C++         |
|  8 | Susan  |   23 | W    |    170 |         5 |  1 | Java        |
|  8 | Susan  |   23 | W    |    170 |         5 |  2 | Mysql       |
|  8 | Susan  |   23 | W    |    170 |         5 |  3 | Python      |
|  8 | Susan  |   23 | W    |    170 |         5 |  4 | Go          |
|  8 | Susan  |   23 | W    |    170 |         5 |  5 | C++         |
|  9 | Thomas |   22 | M    |    178 |         5 |  1 | Java        |
|  9 | Thomas |   22 | M    |    178 |         5 |  2 | Mysql       |
|  9 | Thomas |   22 | M    |    178 |         5 |  3 | Python      |
|  9 | Thomas |   22 | M    |    178 |         5 |  4 | Go          |
|  9 | Thomas |   22 | M    |    178 |         5 |  5 | C++         |
| 10 | Tom    |   23 | M    |    165 |         5 |  1 | Java        |
| 10 | Tom    |   23 | M    |    165 |         5 |  2 | Mysql       |
| 10 | Tom    |   23 | M    |    165 |         5 |  3 | Python      |
| 10 | Tom    |   23 | M    |    165 |         5 |  4 | Go          |
| 10 | Tom    |   23 | M    |    165 |         5 |  5 | C++         |
+----+--------+------+------+--------+-----------+----+-------------+
50 rows in set (0.00 sec)

mysql> select * from tb_course cross join tb_students_info where tb_course.id = tb_students_info.course_id;
+----+-------------+----+--------+------+------+--------+-----------+
| id | course_name | id | name   | age  | sex  | height | course_id |
+----+-------------+----+--------+------+------+--------+-----------+
|  1 | Java        |  1 | Dany   |   25 | W    |    160 |         1 |
|  2 | Mysql       |  2 | Green  |   23 | W    |    158 |         2 |
|  1 | Java        |  3 | Henry  |   23 | M    |    185 |         1 |
|  3 | Python      |  4 | Jane   |   22 | W    |     62 |         3 |
|  2 | Mysql       |  5 | Jim    |   24 | M    |    175 |         2 |
|  4 | Go          |  6 | John   |   21 | M    |    172 |         4 |
|  4 | Go          |  7 | Lily   |   22 | W    |    165 |         4 |
|  5 | C++         |  8 | Susan  |   23 | W    |    170 |         5 |
|  5 | C++         |  9 | Thomas |   22 | M    |    178 |         5 |
|  5 | C++         | 10 | Tom    |   23 | M    |    165 |         5 |
+----+-------------+----+--------+------+------+--------+-----------+
10 rows in set (0.00 sec)

mysql> select tb_course.course_name,tb_students_info.age from tb_course cross jointb_students_info where tb_course.id = tb_students_info.course_id;
+-------------+------+
| course_name | age  |
+-------------+------+
| Java        |   25 |
| Mysql       |   23 |
| Java        |   23 |
| Python      |   22 |
| Mysql       |   24 |
| Go          |   21 |
| Go          |   22 |
| C++         |   23 |
| C++         |   22 |
| C++         |   23 |
+-------------+------+
10 rows in set (0.00 sec)

mysql> 




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