    # File lib/active_record/connection_adapters/oracle_adapter.rb, line 394
            def pk_and_sequence_for(table_name)
              (owner, table_name) = @connection.describe(table_name)

              pks = select_values("select cc.column_name\nfrom all_constraints c, all_cons_columns cc\nwhere c.owner = '\#{owner}'\nand c.table_name = '\#{table_name}'\nand c.constraint_type = 'P'\nand cc.owner = c.owner\nand cc.constraint_name = c.constraint_name\n", 'Primary Key')

              # only support single column keys
              pks.size == 1 ? [oracle_downcase(pks.first), nil] : nil
            end