Merci pour ton retour,
Lors de l'utilisation

 sudo apt remove --purge mysql-server

J'ai ça

 macmada@server_macmada:~$ sudo apt remove --purge mysql-server
[sudo] password for macmada:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libaio1 libevent-core-2.0-5 mysql-client-5.7 mysql-client-core-5.7 mysql-common mysql-server-5.7 mysql-server-core-5.7
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
  mysql-server*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 184 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 74966 files and directories currently installed.)
Removing mysql-server (5.7.18-0ubuntu0.16.04.1) ...
Setting up mysql-server-5.7 (5.7.18-0ubuntu0.16.04.1) ...
Renaming removed key_buffer and myisam-recover options (if present)
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
● mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: exit-code) since Fri 2017-07-07 14:43:42 CEST; 7ms ago
  Process: 1866 ExecStartPost=/usr/share/mysql/mysql-systemd-start post (code=exited, status=0/SUCCESS)
  Process: 1865 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
  Process: 1856 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 1865 (code=exited, status=1/FAILURE)

Jul 07 14:43:42 server_macmada systemd[1]: Failed to start MySQL Community Server.
Jul 07 14:43:42 server_macmada systemd[1]: mysql.service: Unit entered failed state.
Jul 07 14:43:42 server_macmada systemd[1]: mysql.service: Failed with result 'exit-code'.
dpkg: error processing package mysql-server-5.7 (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 mysql-server-5.7
E: Sub-process /usr/bin/dpkg returned an error code (1)
macmada@server_macmada:~$

J'ai réussi en effectuant

 sudo apt-get remove --purge mysql*

après j'ai fait un

 sudo apt-get update

et un

 sudo apt-get install mysql-server 

J'ai :

update-alternatives: using /etc/mysql/mysql.cnf to provide /etc/mysql/my.cnf (my.cnf) in auto mode
Renaming removed key_buffer and myisam-recover options (if present)
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
● mysql.service - MySQL Community Server
   Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: exit-code) since Fri 2017-07-07 15:15:04 CEST; 5ms ago
  Process: 12059 ExecStartPost=/usr/share/mysql/mysql-systemd-start post (code=exited, status=0/SUCCESS)
  Process: 12058 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
  Process: 12049 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
 Main PID: 12058 (code=exited, status=1/FAILURE)

Jul 07 15:15:04 server_macmada systemd[1]: Failed to start MySQL Community S....
Jul 07 15:15:04 server_macmada systemd[1]: mysql.service: Unit entered faile....
Jul 07 15:15:04 server_macmada systemd[1]: mysql.service: Failed with result....
Hint: Some lines were ellipsized, use -l to show in full.
dpkg: error processing package mysql-server-5.7 (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mysql-server:
 mysql-server depends on mysql-server-5.7; however:
  Package mysql-server-5.7 is not configured yet.

dpkg: error processing package mysql-server (--configure):
 dependency problems - leaving unconfigured
Processing triggers for libc-bin (2.23-0ubuntu9) ...
Processing triggers for systemd (229-4ubuntu17) ...
Processing triggers for ureadahead (0.100.0-19) ...
Errors were encountered while processing:
 mysql-server-5.7
 mysql-server
E: Sub-process /usr/bin/dpkg returned an error code (1)
macmada@server_macmada:~$

Sql toujours Hs