public DBFieldIterator indexFieldIterator(int columnIndex) throws IOException {
		synchronized (db) {
			IndexTable indexTable = secondaryIndexes.get(columnIndex);
			if (indexTable == null) {
				throw new IOException("Index required (" + getName() + "," + columnIndex + ")");
			}
			return indexTable.indexIterator();
		}
	}
Iterate over all the unique index field values.  Index values are
returned in an ascending sorted order with the initial iterator position
set to the minimum index value.
@param columnIndex identifies an indexed column.
@return index field iterator.
@throws IOException thrown if IO error occurs
Ghidra/Framework/DB/src/main/java/db/Table.java