help for DB

good day everyone, I'm new to Xcode and I would like to start the first steps with a DB. I have two problems: 1) I have no idea which free practice DB you can use. 2) consequently I am not yet familiar with any use of the DB. I would be useful for an indication of a free DB that can be used with Xcode and possibly an example of code to be able to write and read it. I thank anyone who wants to help me

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more specific to my request: I have written two DBs: 1) Libre Office Base 2) MobiDB Does anyone have experience using any of these? Could you give me an example of an app in XCode to connect, read and write tables of at least one of them? Thank you