/**
* Returns a permutation, if this projection is merely a permutation of its input fields,
* otherwise null.
*/
public Permutation getPermutation() {
final int fieldCount = rowType.getFields().length;
if (fieldCount != getChild().getRowType().getFields().length) {
return null;
}
Permutation permutation = new Permutation(fieldCount);
for (int i = 0; i < fieldCount; ++i) {
if (exps[i] instanceof RexInputRef) {
permutation.set(i, ((RexInputRef) exps[i]).getIndex());
} else {
return null;
}
}
return permutation;
}
/**
* Creates a relational expression which permutes the output fields of a relational expression
* according to a permutation.
*
* <p>Optimizations:
*
* <ul>
* <li>If the relational expression is a {@link CalcRel} or {@link ProjectRel} which is already
* acting as a permutation, combines the new permutation with the old;
* <li>If the permutation is the identity, returns the original relational expression.
* </ul>
*
* <p>If a permutation is combined with its inverse, these optimizations would combine to remove
* them both.
*
* @param rel Relational expression
* @param permutation Permutation to apply to fields
* @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 permutes its input fields
*/
public static RelNode permute(RelNode rel, Permutation permutation, List<String> fieldNames) {
if (permutation.isIdentity()) {
return rel;
}
if (rel instanceof CalcRel) {
CalcRel calcRel = (CalcRel) rel;
Permutation permutation1 = calcRel.getProgram().getPermutation();
if (permutation1 != null) {
Permutation permutation2 = permutation.product(permutation1);
return permute(rel, permutation2, null);
}
}
if (rel instanceof ProjectRel) {
Permutation permutation1 = ((ProjectRel) rel).getPermutation();
if (permutation1 != null) {
Permutation permutation2 = permutation.product(permutation1);
return permute(rel, permutation2, null);
}
}
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 < permutation.getTargetCount(); i++) {
int target = permutation.getTarget(i);
final RelDataTypeField targetField = fields.get(target);
outputTypeList.add(targetField.getType());
outputNameList.add(
((fieldNames == null) || (fieldNames.size() <= i) || (fieldNames.get(i) == null))
? targetField.getName()
: fieldNames.get(i));
exprList.add(rel.getCluster().getRexBuilder().makeInputRef(fields.get(i).getType(), i));
final int source = permutation.getSource(i);
projectRefList.add(new RexLocalRef(source, fields.get(source).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());
}