Function DeterminePossibleValueSet

src/backend/optimizer/util/predtest.c:2323–2355

* * Get the possible values of variable, as determined by the given qualification clause * * Note that only variables whose type is greenplumDbHashtable will return an actual finite set of values. All others * will go to the default behavior -- return that any value is possible * * Note that if there are two variables to check, you must call this twice. This then means that * if the

 *    possible values is within the cross-product of the two variables' sets
 */
PossibleValueSet
DeterminePossibleValueSet(Node *clause, Node *variable, Oid opfamily)
{
	PredIterInfoData clauseInfo;
	PossibleValueSet result;

	if ( clause == NULL )
	{
		InitPossibleValueSetData(&result);
		return result;
	}

	switch (predicate_classify(clause, &clauseInfo))
	{
		case CLASS_AND:
			return ProcessAndClauseForPossibleValues(&clauseInfo, clause, variable, opfamily);
		case CLASS_OR:
			return ProcessOrClauseForPossibleValues(&clauseInfo, clause, variable, opfamily);
		case CLASS_ATOM:
			if (TryProcessExprForPossibleValues(clause, variable, opfamily, &result))
			{
				return result;
			}
			/* can't infer anything, so return that any value is possible */
			InitPossibleValueSetData(&result);
			return result;
	}


	/* can't get here */
	elog(ERROR, "predicate_classify returned a bad value");
	return result;
}