新搭建的服務器，先在Ubuntu上安裝mariadb，後來由於很多權限問題，決定安裝Mysql,在卸載過程中由於未卸載幹凈，導致mysql重裝過程中出現了很多問題。

Reading package lists...Done
Building dependency tree
Reading state information ... Done
mysql-server is already the newest version(5.7.21-0ubuntu0.16.04.1).
You might want to run ‘apt-get -f install‘ to correct these:
The following packages have unmet dependencies:
mysql
 
-server: depends: mysql-server-5.7 but it is not going to be installed
E: Unmet dependencies.Try ‘apt-get -f install‘ with no packages(or specify a solution).

通過閱讀錯誤信息可知，主要是因為依賴關系出現問題，主要思路是重建依賴關系，然後幹凈卸載，最後重裝。

首先，更新系統

sudo apt-get update

然後，修復安裝錯誤，會提示輸入mysql用戶名密碼

sudo apt-get --fix-broken install
 

然後，檢索mysql安裝包，並刪除檢索出的依賴包，然後是刪除/var/lib/mysql,最後重裝mysql。

下面我把檢索到的解決方法展示給大家：

We excute the following commands to solve the above problem:
    1.Get the list of MySQL packages installed on the system by executing the command sudo dpkg -l grep mysql
    2.Remove the packages shown above by executing the command 
      
 
sudo apt-get --purge autoremove <packages from the step 1>
    3. Delete /var/lib/mysql
    4.Try to install mysql again.It should solve your problem.

第二步中的packages如下圖所示：

最後就是更新系統並重裝mysql

sudo apt-get update
sudo apt-get install mysql-server mysql-client

總結：

整體思路還是重建依賴關系，幹凈卸載，更新安裝。希望對遇到相同問題不知所措的小夥伴有所啟發、幫助。謝謝。

Ubuntu重裝mysql錯誤解決