protected QueryIterator execute(OpLeftJoin opLeftJoin, QueryIterator input)
{
QueryIterator left = executeOp(opLeftJoin.getLeft(), input) ;
QueryIterator right = executeOp(opLeftJoin.getRight(), root()) ;
QueryIterator qIter = new QueryIterLeftJoin(left, right, opLeftJoin.getExprs(), execCxt) ;
return qIter ;
}