using databse for "enter name" system

hey guys, i wanted to make in my game "enter your name" system, well i know what i have to do in the inputt field on al of these stuff but i want also to do that player can name himself a name that has been taken, i realized that for this thing i have to save data in some database, but my knowledge at that is actually null, can someone please help me at this little issue or maybe let me know about good tutorial out thare? thank you and sorry for my bad english