Troubles with mysql install on Centos 7

I previously tried to install Percona, MariaDB and mysql. Now I am trying to install mysql:

yum -y install mysql mysql-server

YUM log:

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: ftp.cvut.cz
 * epel: ftp.nluug.nl
 * extras: ftp.cvut.cz
 * rpmforge: ftp.nluug.nl
 * updates: ftp.cvut.cz
Resolving Dependencies
--> Running transaction check
---> Package Percona-Server-server-57.x86_64 0:5.7.11-4.1.el7 will be installed
--> Processing Dependency: Percona-Server-shared-57 for package: Percona-Server-server-57-5.7.11-4.1.el7.x86_64
--> Processing Dependency: Percona-Server-client-57 for package: Percona-Server-server-57-5.7.11-4.1.el7.x86_64
---> Package mariadb.x86_64 1:5.5.44-2.el7.centos will be installed
--> Processing Dependency: mariadb-libs(x86-64) = 1:5.5.44-2.el7.centos for package: 1:mariadb-5.5.44-2.el7.centos.x86_64
Package mariadb-libs is obsoleted by Percona-Server-shared-55, but obsoleting package does not provide for requirements
--> Running transaction check
---> Package Percona-Server-client-57.x86_64 0:5.7.11-4.1.el7 will be installed
---> Package Percona-Server-shared-57.x86_64 0:5.7.11-4.1.el7 will be installed
--> Processing Dependency: Percona-Server-shared-compat-57 for package: Percona-Server-shared-57-5.7.11-4.1.el7.x86_64
---> Package mariadb.x86_64 1:5.5.44-2.el7.centos will be installed
--> Processing Dependency: mariadb-libs(x86-64) = 1:5.5.44-2.el7.centos for package: 1:mariadb-5.5.44-2.el7.centos.x86_64
Package mariadb-libs is obsoleted by Percona-Server-shared-55, but obsoleting package does not provide for requirements
--> Running transaction check
---> Package Percona-Server-shared-compat-57.x86_64 0:5.7.11-4.1.el7 will be installed
---> Package mariadb.x86_64 1:5.5.44-2.el7.centos will be installed
--> Processing Dependency: mariadb-libs(x86-64) = 1:5.5.44-2.el7.centos for package: 1:mariadb-5.5.44-2.el7.centos.x86_64
Package mariadb-libs is obsoleted by Percona-Server-shared-55, but obsoleting package does not provide for requirements
--> Finished Dependency Resolution
Error: Package: 1:mariadb-5.5.44-2.el7.centos.x86_64 (base)
           Requires: mariadb-libs(x86-64) = 1:5.5.44-2.el7.centos
           Available: 1:mariadb-libs-5.5.44-2.el7.centos.x86_64 (base)
               mariadb-libs(x86-64) = 1:5.5.44-2.el7.centos
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

Now Percona and mariadb are removed with their dependencies. Why they are now in dependences?