在CentOS 7上安装mySQL 5.7发现需要三条命令，而不是像以往安装其他软件一样一条yum就搞定，这是为什么呢？
首先我们来看看这三条命令是什么
wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
yum -y install mysql57-community-release-el7-10.noarch.rpm
yum -y install mysql-community-server
这三条命令都在做什么呢？
首先第一条命令，通过wget我们知道是在下载一个rpm的包到本地，这个包就是mySQL的安装包了么？如果是的话，那么后面只需要一条命令就可以安装mysql了，而不是需要两条。
其实是yum的repo里面并没有mySQL的安装源，而对于下载的rpm包的安装，是将两条新的安装源加入到yum repositories。
再运行yum -y install mysql-community-server才是真正的安装mySQL
验证
我们登录到CentOS7的机器，列出当前的yum repo
[root@iZm5e67mdyatjusk69dodoZ ~]# yum repolist
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
repo id repo name status
base/7/x86_64 CentOS-7 10,070
docker-ce-stable/x86_64 Docker CE Stable - x86_64 79
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 13,416
extras/7/x86_64 CentOS-7 412
updates/7/x86_64 CentOS-7 900
repolist: 24,877
好像没有mysql相关的，顺便查一下来确认一下
[root@iZm5e67mdyatjusk69dodoZ ~]# yum search mysql-community-server
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Warning: No matches found for: mysql-community-server
No matches found
OK，确实查不到。那咱们来安装一下通过wget下载的rpm
[root@iZm5e67mdyatjusk69dodoZ ~]# yum -y install mysql57-community-release-el7-10.noarch.rpm
Loaded plugins: fastestmirror
Examining mysql57-community-release-el7-10.noarch.rpm: mysql57-community-release-el7-10.noarch
Marking mysql57-community-release-el7-10.noarch.rpm to be installed
Resolving Dependencies
--> Running transaction check
---> Package mysql57-community-release.noarch 0:el7-10 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
=============================================================================================================================
Package Arch Version Repository Size
=============================================================================================================================
Installing:
mysql57-community-release noarch el7-10 /mysql57-community-release-el7-10.noarch 30 k
Transaction Summary
=============================================================================================================================
Install 1 Package
Total size: 30 k
Installed size: 30 k
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : mysql57-community-release-el7-10.noarch 1/1
Verifying : mysql57-community-release-el7-10.noarch 1/1
Installed:
mysql57-community-release.noarch 0:el7-10
Complete!
现在这个rpm已经装好了，咱们再来看一下yum的repo变成什么样子了
[root@iZm5e67mdyatjusk69dodoZ ~]# yum repolist
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
mysql-connectors-community | 2.5 kB 00:00:00
mysql-tools-community | 2.5 kB 00:00:00
mysql57-community | 2.5 kB 00:00:00
(1/3): mysql-tools-community/x86_64/primary_db | 76 kB 00:00:00
(2/3): mysql57-community/x86_64/primary_db | 224 kB 00:00:00
(3/3): mysql-connectors-community/x86_64/primary_db | 62 kB 00:00:00
repo id repo name status
base/7/x86_64 CentOS-7 10,070
docker-ce-stable/x86_64 Docker CE Stable - x86_64 79
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 13,416
extras/7/x86_64 CentOS-7 412
mysql-connectors-community/x86_64 MySQL Connectors Community 165
mysql-tools-community/x86_64 MySQL Tools Community 115
mysql57-community/x86_64 MySQL 5.7 Community Server 444
updates/7/x86_64 CentOS-7 900
repolist: 25,601
看起来和上面不太一样了，多了几个和mysql相关的repo，那我们试着在搜索一下mysql-community-server
[root@iZm5e67mdyatjusk69dodoZ ~]# yum search mysql-community-server
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
============================================ N/S matched: mysql-community-server ============================================
mysql-community-server.x86_64 : A very fast and reliable SQL database server
Name and summary matches only, use "search all" for everything.
这次找到了，这就是为什么需要三条命令来安装的原因。
参考文档
https://www.digitalocean.com/community/tutorials/how-to-install-mysql-on-centos-7
