Ionic + SQL?

I’ve been using Ionic with Firebase and that has worked well. I’m thinking about developing a new app with a SQL backend. I’m interested in knowing what SQL backend is most popular/easiest to implement. So, what have you all done with a SQL backend?

A php/mysql backend is available through this tutorial : http://masteringionic.com/blog/2016-12-15-using-php-and-mysql-with-ionic/.
I implemented it and it worked perfectly :wink: