How to use trim in select query rails or in sql query - mysql

Question

User.select(:name).group(:name).having("count(*) > 1")
this query works fine to select records having duplicate user name. But problem am facing is when there is space in name.
For example.
recoed1 = "Username"
record2 = "Username "
This are the two records but they are having same name, but above query consider them as different records because space is there in the second record. So while selecting I did not get this record.
Any solution using normal mysql query or rails will do.
OR
How I can strip or trim all the column data first from table using rails/mysql query. Then I can apply above query.

Answer 1

What i would do here is make sure your data is tidy in the first place.
You could put in a pre-validation method to call strip on usernames. You could do it like so
#in lib/trimmer.rb
module Trimmer
# Make a class method available to define space-trimming behavior.
def self.included base
base.extend(ClassMethods)
end
module ClassMethods
# Register a before-validation handler for the given fields to
# trim leading and trailing spaces.
def trimmed_fields *field_list
before_validation do |model|
field_list.each do |field|
model.send("#{field}=", model.send("#{field}").strip) if model.send("#{field}").respond_to?('strip')
end
end
end
end
end
Make sure this module is required, wherever you require things in lib in your config.
Now, you can say, in any models, like so (in this example i'm doing some other fields besides username)
class User < ActiveRecord::Base
include Trimmer
trimmed_fields :username, :email, :first_name, :last_name
...
So, that will fix you going forward. The remaining step is to tidy up your existing data. I would do this in a migration. (again, i'm doing some other fields as an example)
tables_and_cols = {"users" => %w(username email first_name last_name), "foos" => %w(bar baz)}
tables_and_cols.each do |table, cols|
cols.each do |col|
ActiveRecord::Base.connection.execute("update #{tablename} set #{col} = trim(#{col})")
end
end
Now, after doing this trim, you may have some duplicate usernames. You will need to decide how you are going to deal with that, since the records involved are no longer valid. If you haven't publically deployed this yet, ie if you don't have any active real users, then it doesn't matter: you can change the usernames to something else. But if you do have real people using it you will probably need to change the username for some of them and inform them. This is unavoidable if you want to maintain a situation where people can't have spaces at the start or end of their username.

Answer 2

You can use mysql's string functions:
User.select("lower(trim(name))").group("lower(trim(name))").having("count(*) > 1")