Upgrade from Debian's to MariaDB's 10.1 packages fails

• install MariaDB server from default Debian repo on stretch:

  $ sudo apt-get install mariadb-server

  ...

  $ dpkg -l | grep -iE 'maria|mysql'

  ii libdbd-mysql-perl 4.041-1 amd64 Perl5 database interface to the MariaDB/MySQL database

  ii libmariadbclient18:amd64 10.1.21-5 amd64 MariaDB database client library

  ii mariadb-client-10.1 10.1.21-5 amd64 MariaDB database client binaries

  ii mariadb-client-core-10.1 10.1.21-5 amd64 MariaDB database core client binaries

  ii mariadb-common 10.1.21-5 all MariaDB common metapackage

  ii mariadb-server 10.1.21-5 all MariaDB database server (metapackage depending on the latest version)

  ii mariadb-server-10.1 10.1.21-5 amd64 MariaDB database server binaries

  ii mariadb-server-core-10.1 10.1.21-5 amd64 MariaDB database core server files

  ii mysql-common 5.8+1.0.2 all MySQL database common files, e.g. /etc/mysql/my.cnf

• enable MariaDB repo:

  deb http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian stretch main

• install MariaDB:

  $ sudo apt-get install mariadb-server

  Reading package lists... Done

  Building dependency tree

  Reading state information... Done

  The following packages were automatically installed and are no longer required:

  libpq5 libstemmer0d

  Use 'sudo apt autoremove' to remove them.

  The following additional packages will be installed:

  iproute libmariadbclient18 libmysqlclient18 mariadb-client-10.1 mariadb-client-core-10.1 mariadb-common mariadb-server-10.1

  mariadb-server-core-10.1

  Suggested packages:

  mailx mariadb-test netcat-openbsd tinyca

  The following NEW packages will be installed:

  iproute libmysqlclient18

  The following packages will be upgraded:

  libmariadbclient18 mariadb-client-10.1 mariadb-client-core-10.1 mariadb-common mariadb-server mariadb-server-10.1 mariadb-server-core-10.1

  7 upgraded, 2 newly installed, 0 to remove and 214 not upgraded.

  Need to get 12.5 MB of archives.

  After this operation, 419 kB of additional disk space will be used.

The attempt fails with the error:

Unpacking mariadb-server-10.1 (10.1.21+maria-1~stretch) over (10.1.21-5) ...

dpkg: error processing archive /tmp/apt-dpkg-install-p1JA1s/0-mariadb-server-10.1_10.1.21+maria-1~stretch_amd64.deb (--unpack):

 trying to overwrite '/usr/bin/mysql_upgrade', which is also in package mariadb-server-core-10.1 10.1.21-5

dpkg-deb: error: subprocess paste was killed by signal (Broken pipe)

dpkg: regarding .../1-mariadb-server-core-10.1_10.1.21+maria-1~stretch_amd64.deb containing mariadb-server-core-10.1:

 mariadb-server-10.1 conflicts with mysql-server-core-5.5

  mariadb-server-core-10.1 provides mysql-server-core-5.5 and is to be installed.

dpkg: error processing archive /tmp/apt-dpkg-install-p1JA1s/1-mariadb-server-core-10.1_10.1.21+maria-1~stretch_amd64.deb (--unpack):

 conflicting packages - not installing mariadb-server-core-10.1

Selecting previously unselected package iproute.

Preparing to unpack .../2-iproute_1%3a4.9.0-1_all.deb ...

Unpacking iproute (1:4.9.0-1) ...

dpkg: regarding .../3-mariadb-client-core-10.1_10.1.21+maria-1~stretch_amd64.deb containing mariadb-client-core-10.1:

 mariadb-client-10.1 conflicts with mysql-client-core-5.5

  mariadb-client-core-10.1 provides mysql-client-core-5.5 and is to be installed.

dpkg: error processing archive /tmp/apt-dpkg-install-p1JA1s/3-mariadb-client-core-10.1_10.1.21+maria-1~stretch_amd64.deb (--unpack):

 conflicting packages - not installing mariadb-client-core-10.1

dpkg: regarding .../4-mariadb-client-10.1_10.1.21+maria-1~stretch_amd64.deb containing mariadb-client-10.1:

 mariadb-client-core-10.1 conflicts with mysql-client-5.5

  mariadb-client-10.1 provides mysql-client-5.5 and is to be installed.

dpkg: error processing archive /tmp/apt-dpkg-install-p1JA1s/4-mariadb-client-10.1_10.1.21+maria-1~stretch_amd64.deb (--unpack):

 conflicting packages - not installing mariadb-client-10.1

Errors were encountered while processing:

 /tmp/apt-dpkg-install-p1JA1s/0-mariadb-server-10.1_10.1.21+maria-1~stretch_amd64.deb

 /tmp/apt-dpkg-install-p1JA1s/1-mariadb-server-core-10.1_10.1.21+maria-1~stretch_amd64.deb

 /tmp/apt-dpkg-install-p1JA1s/3-mariadb-client-core-10.1_10.1.21+maria-1~stretch_amd64.deb

 /tmp/apt-dpkg-install-p1JA1s/4-mariadb-client-10.1_10.1.21+maria-1~stretch_amd64.deb

E: Sub-process /usr/bin/dpkg returned an error code (1)