jazzc is as always right, a db is nothing more than persistent storage of your applications data. Sorting, retrieval, serving and any other logic is handled by your application. In other words, your application will store and retrieve data from the database and most importantly do something (your application logic here) with that data and present it to you or the user.
Which architecture you pick becomes very important when scaling is involved, handling smaller datasets (for example 100k rows is still fairly small) allows a wider margin of error as far as optimization and so on is concerned. So in your case I'd just go with mysql. Unless again I'm mistaken and you are actually building a massive application here.
It all starts with your programming language of choice (as I've mentioned before), as you would want a db solution that can be tightly integrated into your programming language. Once you've picked a couple of candidates you'll have to take a ton of things into consideration before making your final choice.
At the most fundamental level, you got a choice between an sql and a nosql (not-only-sql) database architecture. Mysql, as you might have guessed, is an sql type database. Whereas couchdb for example takes the nosql approach. The following is all IMHO, but basically, the biggest difference between these two is that an sql solution provides a level of automation whereas a nosql solution, well you are basically in charge of many, many thing manually. These results in a number of benefits as well as drawbacks (as with most things...)
For example, mysql is great as an entry database (not to say that it isnt powerful and couldn't be scaled), as it takes care of a lot of things for you. With a nosql system a lot of those "checks and balances" are removed and it is up to you to set them up yourself. This (again this is all IMHO) allows for generally better scaling and better performance however it's a bit of a double sided gun if you don't know what it is that you are doing exactly.
Again the above description is very, very generalized and there are a great deal of differences between different nosql solutions as well (the same applies for sql solutions too of course). So you should most probably do some further research or consult an experienced developer if you must.
Hope this helps and feel free to drop me a PM if you have further questions.
Cheers