return mk_select(db, insert_joins, cols, conds, distinct_on,

            limit=limit, start=start, default_table=in_tables0)

    def log_ignore(in_col, value):

        db.log_debug('Ignoring rows with '+in_col+' = '+value)

                *mk_main_select(mapping.values()), returning=returning,

                into_ref=into_ref, recover=True)

        except DuplicateKeyException, e:

            old_join_cols = join_cols.copy()

            join_cols.update(util.dict_subset_right_join(mapping, e.cols))

            db.log_debug('Ignoring existing rows, comparing on '+str(join_cols))

            assert join_cols != old_join_cols # avoid infinite loops

            # rerun loop with additional constraints

        except NullValueException, e:

            out_col, = e.cols

            try: in_col = mapping[out_col]

            except KeyError: # no mapping for missing col, so every row invalid

                conds[in_col] = sql_gen.CompareCond(None, '!=')

                # rerun loop with additional constraints

        except FunctionValueException, e:

            assert e.name == sql_gen.unescape_table(out_table)

            out_col = 'value' # assume function param was named "value"

            in_col = mapping[out_col]