code: public Extensions queryByExtension(String extensionName, String tableName,
  			String columnName) throws SQLException {
  
  		QueryBuilder<Extensions, Void> qb = queryBuilder();
  
  		setUniqueWhere(qb.where(), extensionName, true, tableName, true,
  				columnName);
  
  		List<Extensions> extensions = qb.query();
  
  		Extensions extension = null;
  		if (extensions.size() > 1) {
  			throw new GeoPackageException("More than one "
  					+ Extensions.class.getSimpleName()
  					+ " existed for unique combination of Extension Name: "
  					+ extensionName + ", Table Name: " + tableName
  					+ ", Column Name: " + columnName);
  		} else if (extensions.size() == 1) {
  			extension = extensions.get(0);
  		}
  
  		return extension;
  	}
docs: Query by extension name, table name, and column name
  
  @param extensionName
  extension name
  @param tableName
  table name
  @param columnName
  column name
  @return extensions
  @throws SQLException
  upon failure