Do I use SQL or PHP or both for the relations between tables?

Hi

I'm building a website in which you can join leagues, and play against each other. I have learnt some SQL in school, but that was very theoretical. Now I'm trying to build my own website and I'm having problems.

So I have these different tables: users, leagues, league participant, match and some others. Do I define the relation between these tables in SQL, or not. Is editing in PHP enough?

Thanks

Relationships are defined in SQL. You can use PHP to help bring back a result set and make decisions based on that result set.