example docker compose for postgresql with db init script

docker-compose.yml

postgres:
  image: postgres:9.4
  volumes:
    # running multiple files
    - ./init.sql:/docker-entrypoint-initdb.d/init.sql
    - ./schema.sql:/docker-entrypoint-initdb.d/1-schema.sql
    - ./data.sql:/docker-entrypoint-initdb.d/2-data.sql

init.sql

create table sometable(id int);