Which database will use in custom service

Hi,
I want to create four different tables without any relations between them. But, I want to fetch rows from these four tables in a single query. I didn’t get any method to perform this action in iOS SDK. So , I decided to use custom service.
Should I have to create my own database or i have to create tables in backendless ?
Is there any sample code for creating custom service in PHP ?
Thanks & Regards,
Raushan

Need answer

Should I have to create my own database or i have to create tables in backendless ?

It is completely up to you.

Is there any sample code for creating custom service in PHP ?

No, we have not created any sample PHP code yet. It is available for JS and Java though.