macOS Mojave 降级安装 MySQL 5.7

brew update
brew install mysql

We've installed your MySQL database without a root password. To secure it run:
    mysql_secure_installation
MySQL is configured to only allow connections from localhost by default
To connect run:
    mysql -uroot
To have launchd start mysql now and restart at login:
  brew services start mysql
Or, if you don't want/need a background service you can just run:
  mysql.server start

# 正常关闭并删除 MySQL
mysql.server stop
brew services stop mysql
brew remove mysql

# 无法正常删除 MySQL
ps -ax | grep mysql
stop and kill any MySQL processes
brew remove mysql
brew cleanup
sudo rm /usr/local/mysql
sudo rm -rf /usr/local/var/mysql
sudo rm -rf /usr/local/mysql*

# 安装 MySQL 5.7
brew install mysql@5.7
brew link --force mysql@5.7

We've installed your MySQL database without a root password. To secure it run:
    mysql_secure_installation

MySQL is configured to only allow connections from localhost by default

To connect run:
    mysql -uroot

mysql@5.7 is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.

If you need to have mysql@5.7 first in your PATH run:
  echo'export PATH="/usr/local/opt/mysql@5.7/bin:$PATH"'>> ~/.zshrc

For compilers to find mysql@5.7 you may need to set:
  export LDFLAGS="-L/usr/local/opt/mysql@5.7/lib"
  export CPPFLAGS="-I/usr/local/opt/mysql@5.7/include"

For pkg-config to find mysql@5.7 you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/mysql@5.7/lib/pkgconfig"


To have launchd start mysql@5.7 now and restart at login:
  brew services start mysql@5.7
Or, if you don't want/need a background service you can just run:
  /usr/local/opt/mysql@5.7/bin/mysql.server start

# 开机自启动 
brew services restart mysql@5.7
# 设置环境变量 
echo 'export PATH="/usr/local/opt/mysql@5.7/bin:$PATH"' >> ~/.zshrc
# 手动启动和关闭 
/usr/local/opt/mysql@5.7/bin/mysql.server start
/usr/local/opt/mysql@5.7/bin/mysql.server stop

# 使用 MySQLdb ，但是提示 importerror no module named mysqldb
brew install mysql-connector-c
pip install mysql-python

# 可能会出现以下错误，按照提示做即可 
Error: Cannot install mysql because conflicting formulae are installed.
  mysql-connector-c: because both install MySQL client libraries

Please `brew unlink mysql-connector-c` before continuing.

Unlinking removes a formula's symlinks from /usr/local. You can
link the formula again after the install finishes. You can --force this
install, but the build may fail or cause obscure side-effects in the
resulting software.