public DBFieldIterator indexKeyIterator(int columnIndex) throws IOException {
		synchronized (db) {
			IndexTable indexTable = secondaryIndexes.get(columnIndex);
			if (indexTable == null) {
				throw new IOException("Index required (" + getName() + "," + columnIndex + ")");
			}
			return indexTable.keyIterator();
		}
	}
Iterate over all primary keys sorted based upon the associated index key.
@param columnIndex schema column to sort on.
@return primary key iterator
@throws IOException thrown if IO error occurs
Ghidra/Framework/DB/src/main/java/db/Table.java