How do I create a live/online marketplace?

Looking to make an online marketplace where users can buy and sell between themselves.

So if someone buys an item of the market the person selling it would recieve the in game currency.

The game itself will be mostly offline it would be more 'tranactions' that should appear as and when they are done.

For instance. user 1 has bought 100 coal from user 2 so user 2 has recieved 1000 credits for the sale of 1000 coal and the market listing is closed so others cannot buy the same item for the user it was sold from.

Or is user 8 attacked user 5 they would get a notification or attack and credit loss etc...

The game would have a lot of items and player stats which should be live(ish) and players should be able to check each others stats.

Would be mostly text based.

Is a mysql database what i'm looking for?

Been using consructs for years and thought i'd try something new.

I'm pretty useless at explaining things so hope that makes sense :)

SQL would be the correct beginning. With PHP as an "translator"

Another way to archive this is to integrate multiplayer. You could programm a "server" in cronstruct. if you only use text you can use a low update frequenzy so you can support a load of players :) I did this once, all you need is a server with an gui and a browser to run the server side... works pretty well and stable, also saving / backups are not a problem. I personally enjoy this method more, as i can do everything in construct!