Function execTuplesUnequal

src/backend/executor/nodeSubplan.c:659–715

* execTuplesUnequal * Return true if two tuples are definitely unequal in the indicated * fields. * * Nulls are neither equal nor unequal to anything else. A true result * is obtained only if there are non-null fields that compare not-equal. * * slot1, slot2: the tuples to compare (must have same columns!) * numCols: the number of attributes to be examined * matchColIdx: array of attri

 * evalContext: short-term memory context for executing the functions
 */
static bool
execTuplesUnequal(TupleTableSlot *slot1,
				  TupleTableSlot *slot2,
				  int numCols,
				  AttrNumber *matchColIdx,
				  FmgrInfo *eqfunctions,
				  const Oid *collations,
				  MemoryContext evalContext)
{
	MemoryContext oldContext;
	bool		result;
	int			i;

	/* Reset and switch into the temp context. */
	MemoryContextReset(evalContext);
	oldContext = MemoryContextSwitchTo(evalContext);

	/*
	 * We cannot report a match without checking all the fields, but we can
	 * report a non-match as soon as we find unequal fields.  So, start
	 * comparing at the last field (least significant sort key). That's the
	 * most likely to be different if we are dealing with sorted input.
	 */
	result = false;

	for (i = numCols; --i >= 0;)
	{
		AttrNumber	att = matchColIdx[i];
		Datum		attr1,
					attr2;
		bool		isNull1,
					isNull2;

		attr1 = slot_getattr(slot1, att, &isNull1);

		if (isNull1)
			continue;			/* can't prove anything here */

		attr2 = slot_getattr(slot2, att, &isNull2);

		if (isNull2)
			continue;			/* can't prove anything here */

		/* Apply the type-specific equality function */
		if (!DatumGetBool(FunctionCall2Coll(&eqfunctions[i],
											collations[i],
											attr1, attr2)))
		{
			result = true;		/* they are unequal */
			break;
		}
	}

	MemoryContextSwitchTo(oldContext);

	return result;
}