Ошибка при удалении MySQL

# apt-get purge mysql-server mysql-client mysql-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 libmysqlclient20 : Depends: mysql-common (>= 5.5) but it is not going to be installed
 mariadb-common : Depends: mysql-common (>= 5.6.25) but it is not going to be installed
 mysql-client-5.7 : Depends: mysql-common (>= 5.5) but it is not going to be installed
 postfixadmin : Depends: mysql-client but it is not going to be installed or
                         postgresql-client
                Recommends: postfix-mysql but it is not going to be installed or
                            postfix-pgsql but it is not going to be installed
                Recommends: mysql-server or
                            postgresql but it is not going to be installed
                Recommends: zendframework but it is not installable
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

Пробовал делать то, что предлагает:

# apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
  libnet-xwhois-perl linux-headers-4.4.0-24 linux-headers-4.4.0-24-generic
  linux-headers-4.4.0-28 linux-headers-4.4.0-28-generic linux-headers-4.4.0-31
  linux-headers-4.4.0-31-generic linux-headers-4.4.0-34
  linux-headers-4.4.0-34-generic linux-headers-4.4.0-36
  linux-headers-4.4.0-36-generic linux-headers-4.4.0-42
  linux-headers-4.4.0-42-generic linux-image-4.4.0-24-generic
  linux-image-4.4.0-28-generic linux-image-4.4.0-31-generic
  linux-image-4.4.0-34-generic linux-image-4.4.0-36-generic
  linux-image-4.4.0-42-generic mariadb-common
Use 'apt autoremove' to remove them.
The following additional packages will be installed:
  mysql-server-5.7
Suggested packages:
  tinyca
The following NEW packages will be installed:
  mysql-server-5.7
0 upgraded, 1 newly installed, 0 to remove and 15 not upgraded.
24 not fully installed or removed.
Need to get 0 B/2,597 kB of archives.
After this operation, 48.3 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Preconfiguring packages ...
(Reading database ... 293878 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.7_5.7.16-0ubuntu0.16.04.1_amd64.deb ...
Aborting downgrade from (at least) 10.0 to 5.7.
If are sure you want to downgrade to 5.7, remove the file
/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.7_5.7.16-0ubuntu0.16.04.1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
Errors were encountered while processing:
 /var/cache/apt/archives/mysql-server-5.7_5.7.16-0ubuntu0.16.04.1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
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