/* Check if the Scan corresponding to the RelationSchema is already present in the join_operators. */ boolean relationAlreadyContainedInAJoinOperator(BaseRelationSchema rs) { ScanOperator so = findScanOperator(rs); for (JoinOperator jo : join_operators) if ((so == jo.getLeftOperator()) || (so == jo.getRightOperator())) return true; return false; }