branches/zip: row_merge_tuple_cmp(): Do not report a duplicate key value

if any of the fields are NULL.  While the tuples are equal in the
sorting order, SQL NULL is defined to be logically inequal to
anything else. (Bug #41904)

rb://70 approved by Heikki Tuuri

row/row0merge.c

@@ -442,14 +442,29 @@ row_merge_tuple_cmp(
 	int		cmp;
 	const dfield_t*	field	= a;
 
+	/* Compare the fields of the tuples until a difference is
+	found or we run out of fields to compare.  If !cmp at the
+	end, the tuples are equal. */
 	do {
 		cmp = cmp_dfield_dfield(a++, b++);
 	} while (!cmp && --n_field);
 
 	if (UNIV_UNLIKELY(!cmp) && UNIV_LIKELY_NULL(dup)) {
+		/* Report a duplicate value error if the tuples are
+		logically equal.  NULL columns are logically inequal,
+		although they are equal in the sorting order.  Find
+		out if any of the fields are NULL. */
+		for (b = field; b != a; b++) {
+			if (dfield_is_null(b)) {
+
+				goto func_exit;
+			}
+		}
+
 		row_merge_dup_report(dup, field);
 	}
 
+func_exit:
 	return(cmp);
 }