What´s better? Several smaller databases or one large

Question

I am doing application for learning words in foreign language, so I have this words stored in my database. These words are separated for example into 3 levels of difficulty. Every level is made of some groups of words, these groups introduces TABLES of SQLite db. I am using SQLiteOpenHelper as communication between application and databases.

Now my question. What is better?

• Make 3 smaller databases, each for every level and use own SQLiteOpenHelper, so together 3 dbs with 3 open helpers.
• Make 1 large database, where will be that 3 levels, which means many TABLES, but just only 1 SQLiteOpenHelper.

Thanks for any advice or opininon.

Answer 1

I suggest 1 large database (DB).

You should not be worried about making large DBs, DBs are invented to store a large amount of data (and even many-many tables). It is much easier to create and maintain one DB than multiple ones and your code will be much clearer using one DB.

And I don't know your program, but I would go even further: I would rather store all words in the same table if you store the same information of them, and add a column to show the level and another one to show the group which they belong to.

The main idea of SQL is that you don't really care how much space your DB will require and how much time it gonna take to find the result of a query because DataBase Managent Systems (in your case the SQLiteOpenHelper and SQLite) are insanely efficient considering space and time. Instead you should rather concentrate on designing a system that can be expanded easily (for example if you want to add another column to tables containing words (e.g. you want to store a new information about words) or want to add new levels or groups in a later stage of development) and has clear structure. You might lose a few milliseconds separating groups and levels via the SELECT command of SQL, but your DB will be much more flexible - you can add levels and groups and add more information about words with ease. The key of desinging a good DB: You should store different kind of data in different tables and same kind of data in same table...

Answer 2

The error that you mention in your comment is almost certainly a bug in your application code. There is no reason that an application with multiple databases should encounter that sort of error.

That said, my answer to your original question is that it is objectively "better" to use a single database.

It is better because you will have less code to maintain, no possibility of attempting to access the wrong database in a given situation, and the code will be more idiomatic - i.e. there's no benefit to using multiple databases, so if you were to use multiple databases, anyone reading your code would spend a lot of time trying to figure out why you did it.