（こんばんは。前回の投稿から間が空いてしまったので、要点だけ書きますね。）
MySQL 8.0以降は、ユーザ認証方式を mysql_native_password に変更しましょう
理由：mysql 8.0以降はユーザ認証の方式がcaching_sha2_password に変わったが、現行のphp 7.3.9 ではその認証方式がサポートされていないため。
まずは、workspaceコンテナに接続して、PHPバージョン確認します。
$ docker-compose exec workspace bash
root@dee160787a84:/var/www# php -v
PHP 7.3.9-1+ubuntu16.04.1+deb.sury.org+1 (cli) (built: Sep 2 2019 12:54:04) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.9, Copyright (c) 1998-2018 Zend Technologies
with Zend OPcache v7.3.9-1+ubuntu16.04.1+deb.sury.org+1, Copyright (c) 1999-2018, by Zend Technologies
root@dee160787a84:/var/www# exit
exit
MySQLコンテナに接続し、rootでログインします。
$ docker-compose exec mysql bash root@403e510891bb:/# mysql -u root -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 8 Server version: 8.0.17 MySQL Community Server - GPL Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql DATABASE（設定用DB）に入り、ユーザの認証方法を変更します。
mysql> use mysql Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> select user, host, plugin from user; +------------------+-----------+-----------------------+ | user | host | plugin | +------------------+-----------+-----------------------+ | default | % | caching_sha2_password | | root | % | caching_sha2_password | | mysql.infoschema | localhost | caching_sha2_password | | mysql.session | localhost | caching_sha2_password | | mysql.sys | localhost | caching_sha2_password | | root | localhost | caching_sha2_password | +------------------+-----------+-----------------------+ 6 rows in set (0.00 sec) mysql> alter user 'default'@'%' identified with mysql_native_password by 'secret'; Query OK, 0 rows affected (0.11 sec) mysql> select user, host, plugin from user; +------------------+-----------+-----------------------+ | user | host | plugin | +------------------+-----------+-----------------------+ | default | % | mysql_native_password | | root | % | caching_sha2_password | | mysql.infoschema | localhost | caching_sha2_password | | mysql.session | localhost | caching_sha2_password | | mysql.sys | localhost | caching_sha2_password | | root | localhost | caching_sha2_password | +------------------+-----------+-----------------------+ 6 rows in set (0.00 sec) mysql> exit Bye
mysql に default user でログイン（パスワードは先程設定した “secret”）して、default DATABASEを確認できたらOKです。
root@403e510891bb:/# mysql -u default -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 9 Server version: 8.0.17 MySQL Community Server - GPL Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> show databases; +--------------------+ | Database | +--------------------+ | default | | information_schema | +--------------------+ 2 rows in set (0.00 sec) mysql> use default Database changed mysql> show tables; Empty set (0.01 sec) mysql> exit Bye root@403e510891bb:/# exit exit
ちなみに、認証方式が caching_sha2_password のままだとシンタックスエラーが出ます。
mysql> show tables in default; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'default' at line 1
ブラウザで http://localhost:8080 から phpMyAdminを表示させ、mysql, default, secretでログインして、mysqlの内容を表示させることができれば成功です。