database - One big query vs. many small ones?

Question

I'd like to know, which option is the most expensive in terms of bandwith and overall efficiency.

Let's say I have a class Client in my application and a table client in my database.

Is it better to have one static function Client.getById that retrieves the whole client record or many (Client.getNameById, Client.getMobileNumberById, etc.) that retrieve individual fields?

If a single record has a lot of fields and I end up using one or two in the current script, is it still better to retrieve everything and decide inside the application what to do with all the data?

I'm using PHP and MySQL by the way.

Answer 1

Is it better to have one static function Client.getById that retrieves the whole client record or many (Client.getNameById, Client.getMobileNumberById, etc.) that retrieve individual fields?

Yes, it is.

Network latency and lag as well as the overheads of establishing a connection mean that making as small a number of database calls as possible is the best way to keep the database from saturation.

If the size of the data is really so much that you see an effect, you can consider retrieval of the specific fields you need in one single query (tailor the queries to the data).