I have a simple question but could not find answer. Question is that does every account on social website or application have unique social network id. I did found that Facebook users have unique social id but can two different users on different social applications have same social network id.
Thanks
Usually a users unique id would be unique only to it's application. So if you have an account on Facebook you have a user id that is unique to Facebook, if you have an account on Twitter then you have a user id that is unique to Twitter.
Some 'networks' allow you to join or log-in using an account from Facebook/Google/Twitter, etc.. In this case I believe your details are merely (for lack of better word) linked to a new user id on the new site you joined, it just appears you're on your Facebook or whichever account.
Answers to your questions. Yes, every user on every social account have a unique id. Yes (but very unlikely), two different user on two different social websites can have the same id, I get you are asking since you want to store the id in your database, right? :)
Then there is ieedee.com, that gathers all of your id's on one place. One id, for all id's :)