Normally the installation of MySQL can be achieved with a single command, which executes a script provided by MacMiniVault :
bash <(curl -Ls http://git.io/eUx7rg)
However, at the time of writing the script is not compatible with OS X El Capitan (10.11)
An alternative to the aforementioned installation script is installing MySQL using Homebrew. This gist assumes you already have Homebrew installed, if not first read the article "Homebrew and El Capitan"
Make sure Homebrew has the latest formulae, so run brew update
first