/** * 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); }