Remove duplicated `columns` definition

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

@@ -105,10 +105,12 @@ def index_exists?(table_name, column_name, options = {})
         indexes(table_name).any? { |i| checks.all? { |check| check[i] } }
       end
 
-      # Returns an array of Column objects for the table specified by +table_name+.
-      # See the concrete implementation for details on the expected parameter values.
+      # Returns an array of +Column+ objects for the table specified by +table_name+.
       def columns(table_name)
-        raise NotImplementedError, "#columns is not implemented"
+        table_name = table_name.to_s
+        column_definitions(table_name).map do |field|
+          new_column_from_field(table_name, field)
+        end
       end
 
       # Checks to see if a column exists in a given table.

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -162,14 +162,6 @@ def schema_creation
         SchemaCreation.new self
       end
 
-      # Returns an array of +Column+ objects for the table specified by +table_name+.
-      def columns(table_name) # :nodoc:
-        table_name = table_name.to_s
-        column_definitions(table_name).map do |field|
-          new_column_from_field(table_name, field)
-        end
-      end
-
       # this method must only be called while holding connection pool's mutex
       def lease
         if in_use?