What's wrong with this code?

Today I will introduce to you a method from ActiveRecord. The method takes a parameter called type and that value can bu for example :primary_key, :string or :integer. Now, in the first line there is a call to native_database_types. Generally, that call returns a structure that looks somewhat like this:

def native_database_types #:nodoc:
  {
   :primary_key => "int(11) DEFAULT NULL auto_increment PRIMARY KEY",
   :string      => { :name => "varchar", :limit => 255 },
   :text        => { :name => "text" },
   :integer     => { :name => "int", :limit => 11 },
   :float       => { :name => "float" },
   :decimal     => { :name => "decimal" },
   :datetime    => { :name => "datetime" },
   :timestamp   => { :name => "datetime" },
   :time        => { :name => "time" },
   :date        => { :name => "date" },
   :binary      => { :name => "blob" },
   :boolean     => { :name => "tinyint", :limit => 1 }
 }
end

The method itself looks like this.

def type_to_sql(type, limit = nil, precision = nil, scale = nil) #:nodoc:
  native = native_database_types[type]
 column_type_sql = native.is_a?(Hash) ? native[:name] : native
 if type == :decimal # ignore limit, use precison and scale
    precision ||= native[:precision]
   scale ||= native[:scale]
   if precision
     if scale
       column_type_sql << "(#{precision},#{scale})"
     else
       column_type_sql << "(#{precision})"
     end
   else
     raise ArgumentError, "Error adding decimal column: precision cannot be empty if scale if specified" if scale
   end
   column_type_sql
 else
   limit ||= native[:limit]
   column_type_sql << "(#{limit})" if limit
   column_type_sql
 end
end

There is something very wrong with this implementation. Of course, there could exist many errors here, but what I'm thinking about right now is a violation of the usual way methods should work. And in effect, that problem with this method have caused ActiveRecord-JDBC to implement some very inefficient code to handle this method. And it gets called a lot in ActiveRecord. I'll get back later today with a pointer to what's wrong here, and I will also discuss some of what I've done in AR-JDBC to handle this situation. I hope for many suggestions here! =)