1.下載好mysql後，開啟終端

➜  tmp mysql -u root -p                   
Enter password: 

2.直接回車，進入mysql控制檯，設定新密碼　　

  mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('你的新密碼');

3.退出重進，直接回車不輸入密碼，提示密碼錯誤

➜  tmp mysql -u root -p
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

4.輸入剛剛設定的密碼，成功進入

➜  tmp mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.7.27 Homebrew

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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                     |
+------------------------------+
| information_schema           |
| commerce_backend_development |
| commerce_backend_production  |
| commerce_backend_test        |
| mysql                        |
| performance_schema           |
| sys                          |
+------------------------------+
7 rows in set (0.01 sec)