def col_clause(self):
        clause_parts = []
        subvals = []

        if self.interval.start:
            clause_parts.append(self._clause_tmpl.format(self.field, ">="))
            subvals.append(_to_epoch_time(self.interval.start))

        if self.interval.end:
            clause_parts.append(self._clause_tmpl.format(self.field, "<"))
            subvals.append(_to_epoch_time(self.interval.end))

        if clause_parts:
            # One- or two-sided interval.
            clause = ' AND '.join(clause_parts)
        else:
            # Match any date.
            clause = '1'
        return clause, subvals