/**
* Applies a mapping to a collation list.
*
* @param mapping Mapping
* @param collationList Collation list
* @return collation list with mapping applied to each field
*/
public static List<RelCollation> apply(
Mappings.TargetMapping mapping, List<RelCollation> collationList) {
final List<RelCollation> newCollationList = new ArrayList<RelCollation>();
for (RelCollation collation : collationList) {
final List<RelFieldCollation> newFieldCollationList = new ArrayList<RelFieldCollation>();
for (RelFieldCollation fieldCollation : collation.getFieldCollations()) {
final RelFieldCollation newFieldCollation = apply(mapping, fieldCollation);
if (newFieldCollation == null) {
// This field is not mapped. Stop here. The leading edge
// of the collation is still valid (although it's useless
// if it's empty).
break;
}
newFieldCollationList.add(newFieldCollation);
}
// Truncation to collations to their leading edge creates empty
// and duplicate collations. Ignore these.
if (!newFieldCollationList.isEmpty()) {
final RelCollationImpl newCollation = new RelCollationImpl(newFieldCollationList);
if (!newCollationList.contains(newCollation)) {
newCollationList.add(newCollation);
}
}
}
// REVIEW: There might be redundant collations in the list. For example,
// in {(x), (x, y)}, (x) is redundant because it is a leading edge of
// another collation in the list. Could remove redundant collations.
return newCollationList;
}
/** Variant of {@link #trimFields(RelNode, BitSet, Set)} for {@link SortRel}. */
public TrimResult trimFields(SortRel sort, BitSet fieldsUsed, Set<RelDataTypeField> extraFields) {
final RelDataType rowType = sort.getRowType();
final int fieldCount = rowType.getFieldCount();
final RelCollation collation = sort.getCollation();
final RelNode input = sort.getChild();
// We use the fields used by the consumer, plus any fields used as sort
// keys.
BitSet inputFieldsUsed = (BitSet) fieldsUsed.clone();
for (RelFieldCollation field : collation.getFieldCollations()) {
inputFieldsUsed.set(field.getFieldIndex());
}
// Create input with trimmed columns.
final Set<RelDataTypeField> inputExtraFields = Collections.emptySet();
TrimResult trimResult = trimChild(sort, input, inputFieldsUsed, inputExtraFields);
RelNode newInput = trimResult.left;
final Mapping inputMapping = trimResult.right;
// If the input is unchanged, and we need to project all columns,
// there's nothing we can do.
if (newInput == input && inputMapping.isIdentity() && fieldsUsed.cardinality() == fieldCount) {
return new TrimResult(sort, Mappings.createIdentity(fieldCount));
}
final SortRel newSort =
sort.copy(sort.getTraitSet(), newInput, RexUtil.apply(inputMapping, collation));
assert newSort.getClass() == sort.getClass();
// The result has the same mapping as the input gave us. Sometimes we
// return fields that the consumer didn't ask for, because the filter
// needs them for its condition.
return new TrimResult(newSort, inputMapping);
}