here im echoing nothing, what im doing is :
1) obtain email and password
2) query the table "user" to get the mobile number of the specified user info (email and password)
3) query the table "donor" to check if the obtained mobile number exists in the table or no (via $count)
4) if it exists (in other words, $count==1), delete it from the table "donor"
5) if it doesn't (in other words, $count!=1), query the table "user" to get the city where we have a match in email and password
6) insert mobile and city into table "donor"