code: public DataColumnConstraints queryByUnique(String constraintName,
  			DataColumnConstraintType constraintType, String value)
  			throws SQLException {
  
  		DataColumnConstraints constraint = null;
  
  		QueryBuilder<DataColumnConstraints, Void> qb = queryBuilder();
  		setUniqueWhere(qb.where(), constraintName, constraintType, value);
  		List<DataColumnConstraints> constraints = qb.query();
  		if (!constraints.isEmpty()) {
  
  			if (constraints.size() > 1) {
  				throw new GeoPackageException("More than one "
  						+ DataColumnConstraints.class.getSimpleName()
  						+ " was found for unique constraint. Name: "
  						+ constraintName + ", Type: " + constraintType
  						+ ", Value: " + value);
  			}
  
  			constraint = constraints.get(0);
  		}
  
  		return constraint;
  	}
docs: Query by the unique column values
  
  @param constraintName
  constraint name
  @param constraintType
  constraint type
  @param value
  value
  @return data column constraints
  @throws SQLException
  upon failure