这是我的docker-compose.yml文件，其中包含指定的环境变量（root用户名，密码等）。但是，当我运行“ docker-compose up”时，它表示MySQL正在使用空密码进行初始化！

为什么？有解决方法吗？

这是docker-compose.yml

version: '3.3'

services:
  db:
    image: mysql:5.7
          #build: sqldocker
    ports:
           -  "3306:3306"
    environment:
           - MYSQL_ROOT_PASSWORD=123456
           - MYSQL_DATABASE=testdb
           - MYSQL_USER=root
           - MYSQL_PASSWORD=123456
             # volumes:
            # - my-datavolume:/var/lib/mysql
    healthcheck:
           test: ["CMD","mysqladmin","ping"]
           timeout: 20s
           retries: 10
    restart: always
  backendserver:
    build: ./docker-demo-backend/
    ports:
           - "8080:8080"
    links:
           - "db"
    depends_on:
           - "db"
             # restart: always
  frontend:
    build: ./docker-demo-frontend/frontcrud
    links:
           - "backendserver"
    depends_on:
           - "backendserver"
    ports:
           - "80:80"