} else if (rel instanceof SetOpRel) {
// TODO: Handle more than 2 inputs for setop
if (!validSetopParent(rel, parent))
introduceDerivedTable(rel, parent);
SetOpRel setopRel = (SetOpRel) rel;
for (RelNode inputRel : setopRel.getInputs()) {
if (!validSetopChild(inputRel)) {
introduceDerivedTable(inputRel, setopRel);
}
}
} else if (rel instanceof SingleRel) {