How to loop through every record in a Database Table ?

Here is the correct syntax to iterate over all User Table :
Also, to improve performance, you may want to use User.find_each
(see doc) instead of User.all

User.all.each do |user|
  #the code here is called once for each user
  # user is accessible by 'user' variable
end

User.find_each do |user|
  #the code here is called once for each user
  # user is accessible by 'user' variable
end