Plase, make up a list of tests to be enabled after multi-directional
iterators are introduced. Don’t fix tests which fail now, simply comment
them. Finally, add a few simple tests verifying that different sorting
orders are not supported now.

I did as you say. Added list of tests as a comment to #3309.
But I would like to know, why commenting tests & making a list
of them is better than change tests & comment old expected results?
The main advantage is that one can not ignore/miss tests, which
would fail after #3309 is done.

+    -- Tests are commented because of the reason described in
+    -- NOTE at the beginning of the file.
+    -- <begin>
+    --local data = {
+    --    {limit=0, offset=4, orderby="+b,+a"},
+    --    {limit=0, offset=5, orderby="+b,+a"},
+    --    {limit=0, offset=6, orderby="+b,+a"},
+    --    {limit=0, offset=9, orderby="+b,+a"},
+    --    {limit=0, offset=0, orderby="+b,+a"},
+    --    {limit=0, offset=1, orderby="+b,+a"},
+    --    {limit=7, offset=4, orderby="+b,+a"},
+    --    {limit=7, offset=9, orderby="+b,+a”},

+    --    {limit=0, offset=4, orderby="+b DESC,+a"},
+    --    {limit=0, offset=5, orderby="+b DESC,+a"},
+    --    {limit=0, offset=6, orderby="+b DESC,+a"},
+    --    {limit=0, offset=9, orderby="+b DESC,+a"},
+    --    {limit=0, offset=0, orderby="+b DESC,+a"},
+    --    {limit=0, offset=1, orderby="+b DESC,+a"},
+    --    {limit=7, offset=4, orderby="+b DESC,+a"},
+    --    {limit=7, offset=9, orderby="+b DESC,+a"},

+void
+sql_expr_check_sort_orders(struct Parse *parse,
+    const struct ExprList *expr_list)
+{
+ if(expr_list == NULL)
+ return;
+ enum sort_order reference_order = expr_list->a[0].sort_order;
+ for (int i = 1; i < expr_list->nExpr; i++) {
+ assert(expr_list->a[i].sort_order != SORT_ORDER_UNDEF);
+ if (expr_list->a[i].sort_order != reference_order) {
+ diag_set(ClientError, ER_UNSUPPORTED, "ORDER BY",
+  "different sorting orders”);