hi friends. i am new to arduino. i am using UNO board. i am having a great doubt. i am doing a project on nfc shield. so i want to know when the nfc tags are read by the sheild it should compare the ID of tag with sql server using USB and if matched it should go for next loop... what should i do for that... pleasee help me...
You need a way for the Arduino to run a query against the database to see whether a given tag is valid, There are lots of different ways to do that, using a variety of types of connection, but the simplest would be to connect the Arduino to the PC via a USB cable and have the Arduino send a textual message to the PC containing the tag to be checked, and have an application on the PC read the message, do the database lookup and send a textual message back containing the result. The Arduino would then read and process the result and carry on with whatever other behaviour you want.
There are lots of ways to implement the PC application too, and which one is best for you would depend on what languages you're familiar with and what operating system your PC runs. If it's a Windows based system you have the option of using Gobetwino to perform the lookup, which would mean you don't need to write any code on the PC.