Unable to correct problems, you have held broken packages(mariadb)

$ apt install mariadb-server=1:10.2.31+maria~bionic

遇到錯誤訊息

The following packages have unmet dependencies: mariadb-server : Depends: mariadb-server-10.2 (>= 1:10.2.31+maria~bionic) but it is not going to be installed E: Unable to correct problems, you have held broken packages.

這時候改用

$ aptitude install mariadb-server=1:10.2.31+maria~bionic

解決!!