EDIT

		Set<Integer> result = new HashSet<Integer>();

		String parentCol = "tu_parent";

		String accCol = " tu_acctaxon";

		String tuFk = "tu_id";

		String taxonTable = "tu";

		String vernacularsTable = "vernaculars";

		String distributionTable = "dr";

		String sql = " SELECT DISTINCT %s FROM %s  " +

				" UNION  SELECT DISTINCT %s FROM %s " +

				" UNION  SELECT DISTINCT %s FROM %s " +

				" UNION  SELECT DISTINCT %s FROM %s ";

		sql = String.format(sql, 

				parentCol, taxonTable, 

				accCol, taxonTable,

				tuFk, vernacularsTable,

				tuFk, distributionTable);