public Integer mapRow(ResultSet rs, int rowNum) throws SQLException {
		// Validate column count.
		ResultSetMetaData metaData = rs.getMetaData();
		int nrOfColumns = metaData.getColumnCount();
		if (nrOfColumns != 1) {
			throw new CountRowNumberException("返回记录数过多:期望1条, 实际" + nrOfColumns + "条");
		}
		return rs.getInt(1);
	}