existing mysql docker db

[eddyizm]

I have another docker-compose mysql up and running. Created a database, osticket,

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS 7df1425f37f1 mysql:5.7.21 "docker-entrypoint.s…" 2 hours ago Up 2 hours 0.0.0.0:3306->3306/tcp,

I'm a little confused, do I need to attach it in a psuedo container like in he first example

docker run --name osticket_mysql -d -e MYSQL_ROOT_PASSWORD=secret \ -e MYSQL_USER=osticket -e MYSQL_PASSWORD=secret -e MYSQL_DATABASE=osticket mariadb

how do the external db settings get passed to the docker run file?