Arshads-MacBook-Air:~ Arshi$ mysql.server start
/usr/local/bin/mysql.server: line 256: my_print_defaults: command not found
/usr/local/bin/mysql.server: line 276: cd: @@HOMEBREW_CELLAR@@/mysql/5.6.21: No such file or directory
Starting MySQL
 ERROR! Couldn't find MySQL server (@@HOMEBREW_CELLAR@@/mysql/5.6.21/bin/mysqld_safe)

**Mysql has been installed.**

Arshads-MacBook-Air:~ Arshi$ brew install mysql
Warning: mysql-5.6.21 already installed

sudo brew uninstall mysql
sudo brew install mysql

which mysql

$ sudo nano ~/.bash_profile

alias mysql=/usr/local/opt/mysql@5.7/bin/mysql