docker container with own mysql or global docker mysql

Question

We are using docker a lot with our production. Current solution is to use docker with docker-compose setting like this:

   version: '2'
    services:
        service:
            build:
                context: .
                dockerfile: Dockerfile
            expose:
            - 3000
            links:
            - mysql
            environment:
            - DB_HOST=mysql
            - DB_DATABASE=test
            - DB_PORT=3306
            - DB_PASSWORD=test
            - DB_USER=test
        mysql:
            image: mysql:5.7
            environment:
            - MYSQL_ROOT_PASSWORD=test
            - MYSQL_DATABASE=test
            - MYSQL_USER=test
            - MYSQL_PASSWORD=test
            restart: always
            volumes:

Question is should we use container based mysql like we use? Or should we make an global msyql docker container and link the all containers to that mysql?

What are the best practices for concerning memory and cpu consumption?