Docker execute MySQL query on start-up and output results

if you're using official mysql docker image then

https://hub.docker.com/_/mysql

When a container is started for the first time, a new database with the specified name will be created and initialized with the provided configuration variables. Furthermore, it will execute files with extensions **.sh, .sql and .sql.gz** that are found in /docker-entrypoint-initdb.d. Files will be executed in alphabetical order. You can easily populate your mysql services by mounting a SQL dump into that directory and provide custom images with contributed data. SQL files will be imported by default to the database specified by the MYSQL_DATABASE variable.

Here is example, you can even run custom shell scripts, with shared volume your php container can easily access file generated.

version : '3'
services:
  mysql:
    image: mysql:latest
    environment:
      MYSQL_ROOT_PASSWORD: mysecretpassword
    ports:
      - "3306:3306"
    volumes:
      - "./scripts/add-my-schema.sql:/docker-entrypoint-initdb.d/1.sql"
      - "./scripts/add-data-to-it.sql:/docker-entrypoint-initdb.d/2.sql"
      - "./scripts/generate-some-output.sh:/docker-entrypoint-initdb.d/process.sh"

Here is reference to https://github.com/docker-library/mysql/blob/master/8.0/docker-entrypoint.sh#L56

It contains

# usage: docker_process_init_files [file [file [...]]]
#    ie: docker_process_init_files /always-initdb.d/*
# process initializer files, based on file extensions
docker_process_init_files() {
    # mysql here for backwards compatibility "${mysql[@]}"
    mysql=( docker_process_sql )

    echo
    local f
    for f; do
        case "$f" in
            *.sh)
                # https://github.com/docker-library/postgres/issues/450#issuecomment-393167936
                # https://github.com/docker-library/postgres/pull/452
                if [ -x "$f" ]; then
                    mysql_note "$0: running $f"
                    "$f"
                else
                    mysql_note "$0: sourcing $f"
                    . "$f"
                fi
                ;;
            *.sql)    mysql_note "$0: running $f"; docker_process_sql < "$f"; echo ;;
            *.sql.gz) mysql_note "$0: running $f"; gunzip -c "$f" | docker_process_sql; echo ;;
            *.sql.xz) mysql_note "$0: running $f"; xzcat "$f" | docker_process_sql; echo ;;
            *)        mysql_warn "$0: ignoring $f" ;;
        esac
        echo
    done
}