The best way to learn this stuff is to learn how it works for all games, not just FIFA.
EA, most other companies, and most databases use a process called data normalization. One way to identify that data is normalized is that no simple piece of data will ever be stored twice.
Imagine I wanted to make a table with a player's name, country of origin and their position.
I could write out...
Bob Smith, USA, Defender
Mark Poncy, UK, Defender
Erin Brockofacer, USA, Striker
But I'm wasting a ton of data repeating country names and positions. Also, what if another Bob Smith comes along? That's a common name. It's highly probably that at some point another Bob Smith from the United States who plays defender gets added to my database. Now I have no way to distinguish between those two rows.
Instead, let me make three tables. Nations. Positions. Players.
Within each table, let's make sure that each row has a unique Id that never repeats in any other row.
1 , USA
2 , UK
3 , Brazil
1 , defender
2 , midfielder
3 , striker
PlayerId, name , nation, position
1 , Bob Smith, 1 , 1
2 , Mark Ponce, 2 , 1
3. , Erin Brockerface, 1, 3
Now, we stopped repeating 'USA' and 'defender. Everything is stored only once. The database structure and the exe builds the interrelationships. It might say, 'I see that Bob Smith is from country 1, what is country 1? I see that it is the United States. I'll show the user, "United States."'
Now what if we have one player on two teams? Do we store that player twice? Hell no. Enormous waste of space. Instead, let's build another table that just links a player to a team.
UniqueId, playerId, teamId
1 , 2 , 130010
That would link Mark Ponce to a team with Id 130010.
When you go to make a team, it will be created in a very similar way but with a table set aside to link the team and league.
Preserves data, minimizes data storage. Maximizes pliability.
This is data in the third normal form and you can read more about it here. It's a very common, very efficient form of data normalization. Starting to see how it works?