Example #1
0
 /**
  * Creates a relational expression which projects the output fields of a relational expression
  * according to a partial mapping.
  *
  * <p>A partial mapping is weaker than a permutation: every target has one source, but a source
  * may have 0, 1 or more than one targets. Usually the result will have fewer fields than the
  * source, unless some source fields are projected multiple times.
  *
  * <p>This method could optimize the result as {@link #permute} does, but does not at present.
  *
  * @param rel Relational expression
  * @param mapping Mapping from source fields to target fields. The mapping type must obey the
  *     constaints {@link MappingType#isMandatorySource()} and {@link
  *     MappingType#isSingleSource()}, as does {@link MappingType#InverseFunction}.
  * @param fieldNames Field names; if null, or if a particular entry is null, the name of the
  *     permuted field is used
  * @return relational expression which projects a subset of the input fields
  */
 public static RelNode projectMapping(RelNode rel, Mapping mapping, List<String> fieldNames) {
   assert mapping.getMappingType().isSingleSource();
   assert mapping.getMappingType().isMandatorySource();
   if (mapping.isIdentity()) {
     return rel;
   }
   final List<RelDataType> outputTypeList = new ArrayList<RelDataType>();
   final List<String> outputNameList = new ArrayList<String>();
   final List<RexNode> exprList = new ArrayList<RexNode>();
   final List<RexLocalRef> projectRefList = new ArrayList<RexLocalRef>();
   final List<RelDataTypeField> fields = rel.getRowType().getFieldList();
   for (int i = 0; i < fields.size(); i++) {
     final RelDataTypeField field = fields.get(i);
     exprList.add(rel.getCluster().getRexBuilder().makeInputRef(field.getType(), i));
   }
   for (int i = 0; i < mapping.getTargetCount(); i++) {
     int source = mapping.getSource(i);
     final RelDataTypeField sourceField = fields.get(source);
     outputTypeList.add(sourceField.getType());
     outputNameList.add(
         ((fieldNames == null) || (fieldNames.size() <= i) || (fieldNames.get(i) == null))
             ? sourceField.getName()
             : fieldNames.get(i));
     projectRefList.add(new RexLocalRef(source, sourceField.getType()));
   }
   final RexProgram program =
       new RexProgram(
           rel.getRowType(),
           exprList,
           projectRefList,
           null,
           rel.getCluster().getTypeFactory().createStructType(outputTypeList, outputNameList));
   return new CalcRel(
       rel.getCluster(),
       rel.getTraitSet(),
       rel,
       program.getOutputRowType(),
       program,
       Collections.<RelCollation>emptyList());
 }
 public MappingType getMappingType() {
   return parent.getMappingType().inverse();
 }