How to check existed data in firebase?

Question

I am using firebase database, but I am newbie with it. I am following this tutorial,

Now, my question is how can I check the email if it is already exist in the data

Answer 1

Inside ValueEventListener() check email address is exist or not Try this

if(!dataSnapshot.child("users").child("email").exist)

then insert new value

Answer 2

If you are trying to create a rule for block user have 2 accounts with same email, you can use the rules inside firebase. There are rules ready for this.

Authentication -> Method -> botton functions.