Function ExecEvalRowNullInt

src/backend/executor/execExprInterp.c:2700–2778

Common code for IS [NOT] NULL on a row value */

/* Common code for IS [NOT] NULL on a row value */
static void
ExecEvalRowNullInt(ExprState *state, ExprEvalStep *op,
				   ExprContext *econtext, bool checkisnull)
{
	Datum		value = *op->resvalue;
	bool		isnull = *op->resnull;
	HeapTupleHeader tuple;
	Oid			tupType;
	int32		tupTypmod;
	TupleDesc	tupDesc;
	HeapTupleData tmptup;

	*op->resnull = false;

	/* NULL row variables are treated just as NULL scalar columns */
	if (isnull)
	{
		*op->resvalue = BoolGetDatum(checkisnull);
		return;
	}

	/*
	 * The SQL standard defines IS [NOT] NULL for a non-null rowtype argument
	 * as:
	 *
	 * "R IS NULL" is true if every field is the null value.
	 *
	 * "R IS NOT NULL" is true if no field is the null value.
	 *
	 * This definition is (apparently intentionally) not recursive; so our
	 * tests on the fields are primitive attisnull tests, not recursive checks
	 * to see if they are all-nulls or no-nulls rowtypes.
	 *
	 * The standard does not consider the possibility of zero-field rows, but
	 * here we consider them to vacuously satisfy both predicates.
	 */

	tuple = DatumGetHeapTupleHeader(value);

	tupType = HeapTupleHeaderGetTypeId(tuple);
	tupTypmod = HeapTupleHeaderGetTypMod(tuple);

	/* Lookup tupdesc if first time through or if type changes */
	tupDesc = get_cached_rowtype(tupType, tupTypmod,
								 &op->d.nulltest_row.rowcache, NULL);

	/*
	 * heap_attisnull needs a HeapTuple not a bare HeapTupleHeader.
	 */
	tmptup.t_len = HeapTupleHeaderGetDatumLength(tuple);
	tmptup.t_data = tuple;

	for (int att = 1; att <= tupDesc->natts; att++)
	{
		/* ignore dropped columns */
		if (TupleDescAttr(tupDesc, att - 1)->attisdropped)
			continue;
		if (heap_attisnull(&tmptup, att, tupDesc))