Function isJoinExprNull

src/backend/executor/execExpr.c:4322–4349

---------------------------------------------------------------- * isJoinExprNull * * Checks if the join expression evaluates to NULL for a given * input tuple. * * The input tuple has to be present in the correct TupleTableSlot * in the ExprContext. For example, if all the expressions * in joinExpr refer to the inner side of the join, * econtext->ecxt_innertuple must be valid. * -------

 * ----------------------------------------------------------------
 */
bool
isJoinExprNull(List *joinExpr, ExprContext *econtext)
{
	ListCell   *lc;
	bool		joinkeys_null = true;

	Assert(joinExpr != NIL);

	foreach(lc, joinExpr)
	{
		ExprState  *keyexpr = (ExprState *) lfirst(lc);
		bool		isNull = false;

		/*
		 * Evaluate the current join attribute value of the tuple
		 */
		ExecEvalExpr(keyexpr, econtext, &isNull);

		if (!isNull)
		{
			/* Found at least one non-null join expression, we're done */
			joinkeys_null = false;
			break;
		}
	}

	return joinkeys_null;
}