pg is the only adapter that supports the xml type, so push the method down

activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb

@@ -72,15 +72,6 @@ def initialize(base)
         @base = base
       end
 
-      def xml(*args)
-        raise NotImplementedError unless %w{
-          sqlite mysql mysql2
-        }.include? @base.adapter_name.downcase
-
-        options = args.extract_options!
-        column(args[0], :text, options)
-      end
-
       # Appends a primary key definition to the table definition.
       # Can be called multiple times, but this is probably not a good idea.
       def primary_key(name)

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -338,6 +338,10 @@ def column(name, type = nil, options = {})
           self
         end
 
+        def xml(options = {})
+          column(args[0], :text, options)
+        end
+
         private
 
         def create_column_definition(base, name, type)