The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink include/mysql
/usr/local/include is not writable.

You can try again using:
  brew link mysql

原因：无法写入 /usr/local/include 文件夹
解决方法：
去 /usr/local/include 看看
我的 /usr/local 下面并没有 include 文件夹，于是我就新建了一个；然后再使用 brew link mysql，这次报错：

Error: Could not symlink lib/libmysqlclient.20.dylib
/usr/local/lib is not writable.

我的 /usr/local 下面并没有 lib 文件夹，于是我就新建了一个 lib
再次运行 brew link mysql 就成功了。

mysqld_safe A mysqld process already exists

要卸载干净的话，要写在很多地方，否则会影响下一次安装；
比如偏好设置、开机启动设置等，也要卸载哦。

brew remove mysql  
brew cleanup  
launchctl unload -w ~/Library/LaunchAgents/com.mysql.mysqld.plist  
rm ~/Library/LaunchAgents/com.mysql.mysqld.plist  

sudo rm /usr/local/mysql
sudo rm -rf /usr/local/mysql*
sudo rm -rf /Library/StartupItems/MySQLCOM
sudo rm -rf /Library/PreferencePanes/My*

rm -rf ~/Library/PreferencePanes/My*

sudo rm -rf /Library/Receipts/mysql*
sudo rm -rf /Library/Receipts/MySQL*
sudo rm -rf /private/var/db/receipts/*mysql*

vim /etc/hostconfig  
edit /etc/hostconfig and remove the line MYSQLCOM=-YES-

• 从 cmd 进入 mysql 命令行模式
  mysql -uroot -p
  输入密码，即可进入

• 退出
  mysql>exit;

• 查看数据库
  mysql> show databases
  结果：

    -> ;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| db_demo0           |
| db_demo1           |
| sys                |
+--------------------+

• 创建数据库 db_demo1
  mysql>create database db_demo1 charset utf8;

• 关闭数据库
  mysql>drop database db_demo1

• 查看表

mysql> use db_demo0; # 进入数据库db_demo0
mysql> show tables;

• 查看 users表的字段信息
  mysql> desc users;