presto-main/src/main/java/io/prestosql/sql/planner/InputExtractor.java/InputExtractor/visitIndexSource
class InputExtractor:        @Override
        public Void visitIndexSource(IndexSourceNode node, Void context)
        {
            TableHandle tableHandle = node.getTableHandle();

            Set<Column> columns = new HashSet<>();
            for (ColumnHandle columnHandle : node.getAssignments().values()) {
                columns.add(createColumn(metadata.getColumnMetadata(session, tableHandle, columnHandle)));
            }

            inputs.add(createInput(session, tableHandle, columns));

            return null;
        }