public DBFieldIterator indexFieldIterator(Field minField, Field maxField, Field startField,
			boolean before, int columnIndex) throws IOException {
		synchronized (db) {
			IndexTable indexTable = secondaryIndexes.get(columnIndex);
			if (indexTable == null) {
				throw new IOException("Index required (" + getName() + "," + columnIndex + ")");
			}
			return indexTable.indexIterator(minField, maxField, startField, before);
		}
	}
Iterate over all the unique index field values within the specified range identified
by minField and maxField.  Index values are returned in an ascending sorted order with the 
initial iterator position corresponding to the startField.
@param minField minimum index column value, if null absolute minimum is used
@param maxField maximum index column value, if null absolute maximum is used
@param startField index column value corresponding to initial position of iterator
@param before if true initial position is before startField value, else position
is after startField value
@param columnIndex identifies an indexed column.
@return index field iterator.
@throws IOException if a secondary index does not exist for the specified
column or an I/O error occurs.
Ghidra/Framework/DB/src/main/java/db/Table.java