/**
* Creates an expression which references correlating variable <code>
* correlName</code> from the context of <code>rel</code>. For example, if <code>correlName</code>
* is set by the 1st child of <code>rel</code>'s 2nd child, then this method returns <code>
* $input2.$input1</code>.
*/
public Expression makeReference(String correlName, RelNode rel) {
JavaFrame frame = (JavaFrame) mapCorrel2Frame.get(correlName);
assert (frame != null);
assert Util.equal(frame.rel.getCorrelVariable(), correlName);
assert (frame.hasVariable());
return frame.getVariable();
}
/**
* Returns the variable which, in the generated program, will hold the current row of a given
* relational expression. This method is only applicable if the relational expression is the
* current one or an input; if it is an ancestor, there is no current value, and this method
* returns null.
*/
public Variable findInputVariable(RelNode rel) {
while (true) {
JavaFrame frame = (JavaFrame) mapRel2Frame.get(rel);
if ((frame != null) && frame.hasVariable()) {
return frame.getVariable();
}
List<RelNode> inputs = rel.getInputs();
if (inputs.size() == 1) {
rel = inputs.get(0);
} else {
return null;
}
}
}