/**
* Creates projection list for scan. If the projection contains expressions, then the input
* references from those expressions are extracted and that list of references becomes the
* projection list.
*
* @param origScan row scan underneath the project
* @param projRel ProjectRel that we will be creating the projection for
* @param projectedColumns returns a list of the projected column ordinals, if it is possible to
* project
* @param preserveExprCondition condition that identifies special expressions that should be
* preserved in the projection
* @param defaultExpr expression to be used in the projection if no fields or special columns are
* selected
* @param newProjList returns a new projection RelNode corresponding to a projection that now
* references a rowscan that is projecting the input references that were extracted from the
* original projection expressions; if the original expression didn't contain expressions,
* then this list is returned empty
* @return true if columns in projection list from the scan need to be renamed
*/
public boolean createProjectionList(
FennelRel origScan,
ProjectRel projRel,
List<Integer> projectedColumns,
PushProjector.ExprCondition preserveExprCondition,
RexNode defaultExpr,
List<ProjectRel> newProjList) {
// REVIEW: what about AnonFields?
int n = projRel.getChildExps().length;
RelDataType rowType = origScan.getRowType();
RelDataType projType = projRel.getRowType();
RelDataTypeField[] projFields = projType.getFields();
List<Integer> tempProjList = new ArrayList<Integer>();
boolean needRename = false;
for (int i = 0; i < n; ++i) {
RexNode exp = projRel.getChildExps()[i];
List<String> origFieldName = new ArrayList<String>();
Integer projIndex = mapProjCol(exp, origFieldName, rowType);
if (projIndex == null) {
// there are expressions in the projection; we need to extract
// all input references and any special expressions from the
// projection
PushProjector pushProject =
new PushProjector(projRel, null, origScan, preserveExprCondition);
ProjectRel newProject = pushProject.convertProject(defaultExpr);
if (newProject == null) {
// can't do any further projection
return false;
}
newProjList.add(newProject);
// using the input references we just extracted, it should now
// be possible to create a projection for the row scan
needRename =
createProjectionList(
origScan,
(ProjectRel) newProject.getChild(),
projectedColumns,
preserveExprCondition,
defaultExpr,
newProjList);
assert (projectedColumns.size() > 0);
return needRename;
}
String projFieldName = projFields[i].getName();
if (!projFieldName.equals(origFieldName.get(0))) {
needRename = true;
}
tempProjList.add(projIndex);
}
// now that we've determined it is possible to project, add the
// ordinals to the return list
projectedColumns.addAll(tempProjList);
return needRename;
}
public void onMatch(RelOptRuleCall call) {
ProjectRel project = (ProjectRel) call.rels[0];
List<RexNode> expList = new ArrayList<RexNode>(Arrays.asList(project.getChildExps()));
if (reduceExpressions(project, expList)) {
call.transformTo(
new ProjectRel(
project.getCluster(),
project.getChild(),
expList.toArray(new RexNode[expList.size()]),
project.getRowType(),
ProjectRel.Flags.Boxed,
Collections.<RelCollation>emptyList()));
// New plan is absolutely better than old plan.
call.getPlanner().setImportance(project, 0.0);
}
}