Install Apache on Debian VPS & unmet dependencies error

Question

I have a VPS and it runs on Debian GNU/Linux 8 (jessie). I try to install Apache, PHP, and MySQL on it. I get the below error:

The following packages have unmet dependencies: mysql-server : Depends: mysql-server-5.5 but it is not going to be installed E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

When I run apt-get -f install , i get below error:

Preconfiguring packages ...
(Reading database ... 39521 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.5_5.5.52-0+deb8u1_amd64.deb ...
Aborting downgrade from (at least) 10.0 to 5.5.
If are sure you want to downgrade to 5.5, remove the file
/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.5_5.5.52-0+deb8u1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
E: Sub-process /usr/bin/dpkg returned an error code (1)

I have basic knowledge of Linux, so any suggestion or help. I search online and try to uninstall and remove and reinstall MySQL... but no luck.

Answer 1

from you error output i did a quick apt-cache search to see the version numbers of mysql-server

from what i seen you might have installed mariadb-server-10.0 installed instead of mysql-server

do a dpkg -l | grep mysql dpkg -l | grep mysql and look at the results. you could also try dpkg -l | grep server dpkg -l | grep server and look at that output also.

ADDED COMMENT-

did you remove the file that it's asking you to do?

if you need to have both db-servers running i would follow along with this
https://superuser.com/questions/1029228/mysql-and-mariadb-instances-on-the-same-server

if you don't need both dbs, then i would apt-get remove mariadb-.. from your server and then apt-get -f install to get mysql-server installed