I really hesitate to help you with such messages...
So I'll let you search, but here is what you should look at :
The following packages have unmet dependencies:
mariadb-client-10.2 : Depends: mariadb-client-core-10.2 (>= 10.2.36+maria~stretch) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.\Zn