MDEV-11746: Wrong result upon using FIRST_VALUE with a window frame

The same approach is needed for LAST_VALUE, otherwise the LAST_VALUE sum
functions are not cleared correctly. Now LAST_VALUE behaves as NTH_VALUE
with 0 offset, only that the frame that it is examining is the bottom bound,
not the top bound.

mysql-test/r/win_first_last_value.result

@@ -113,17 +113,19 @@ last_value(i) OVER (order by i rows between CURRENT ROW and 1 FOLLOWING) as last
 first_value(i) OVER (order by i rows between 1 PRECEDING AND 1 FOLLOWING) as fst_1p1f,
 last_value(i) OVER (order by i rows between 1 PRECEDING AND 1 FOLLOWING) as fst_1p1f,
 first_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p,
-last_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p
+last_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p,
+first_value(i) OVER (order by i rows between 1 FOLLOWING AND 2 FOLLOWING) as fst_1f2f,
+last_value(i) OVER (order by i rows between 1 FOLLOWING AND 2 FOLLOWING) as fst_1f2f
 from t1;
-i	fst_1f	last_1f	fst_1p1f	fst_1p1f	fst_2p1p	fst_2p1p
-1	1	2	1	2	NULL	NULL
-2	2	3	1	3	1	1
-3	3	4	2	4	1	2
-4	4	5	3	5	2	3
-5	5	6	4	6	3	4
-6	6	7	5	7	4	5
-7	7	8	6	8	5	6
-8	8	9	7	9	6	7
-9	9	10	8	10	7	8
-10	10	10	9	10	8	9
+i	fst_1f	last_1f	fst_1p1f	fst_1p1f	fst_2p1p	fst_2p1p	fst_1f2f	fst_1f2f
+1	1	2	1	2	NULL	NULL	2	3
+2	2	3	1	3	1	1	3	4
+3	3	4	2	4	1	2	4	5
+4	4	5	3	5	2	3	5	6
+5	5	6	4	6	3	4	6	7
+6	6	7	5	7	4	5	7	8
+7	7	8	6	8	5	6	8	9
+8	8	9	7	9	6	7	9	10
+9	9	10	8	10	7	8	10	10
+10	10	10	9	10	8	9	NULL	NULL
 drop table t1;

mysql-test/t/win_first_last_value.test

@@ -69,7 +69,9 @@ select i,
        first_value(i) OVER (order by i rows between 1 PRECEDING AND 1 FOLLOWING) as fst_1p1f,
        last_value(i) OVER (order by i rows between 1 PRECEDING AND 1 FOLLOWING) as fst_1p1f,
        first_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p,
-       last_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p
+       last_value(i) OVER (order by i rows between 2 PRECEDING AND 1 PRECEDING) as fst_2p1p,
+       first_value(i) OVER (order by i rows between 1 FOLLOWING AND 2 FOLLOWING) as fst_1f2f,
+       last_value(i) OVER (order by i rows between 1 FOLLOWING AND 2 FOLLOWING) as fst_1f2f
 from t1;
 
 drop table t1;

sql/sql_window.cc

@@ -2311,11 +2311,6 @@ void add_special_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
       fc->add_sum_func(item_sum);
       cursor_manager->add_cursor(fc);
       break;
-    case Item_sum::LAST_VALUE_FUNC:
-      fc= get_frame_cursor(thd, spec, false);
-      fc->add_sum_func(item_sum);
-      cursor_manager->add_cursor(fc);
-      break;
     case Item_sum::LEAD_FUNC:
     case Item_sum::LAG_FUNC:
     {
@@ -2355,6 +2350,22 @@ void add_special_frame_cursors(THD *thd, Cursor_manager *cursor_manager,
       cursor_manager->add_cursor(fc);
       break;
     }
+    case Item_sum::LAST_VALUE_FUNC:
+    {
+      Frame_cursor *bottom_bound= get_frame_cursor(thd, spec, false);
+      Frame_cursor *top_bound= get_frame_cursor(thd, spec, true);
+      cursor_manager->add_cursor(bottom_bound);
+      cursor_manager->add_cursor(top_bound);
+      DBUG_ASSERT(item_sum->fixed);
+      Item *offset_item= new (thd->mem_root) Item_int(thd, 0);
+      offset_item->fix_fields(thd, &offset_item);
+      fc= new Frame_positional_cursor(*bottom_bound,
+                                      *top_bound, *bottom_bound,
+                                      *offset_item, false);
+      fc->add_sum_func(item_sum);
+      cursor_manager->add_cursor(fc);
+      break;
+    }
     case Item_sum::NTH_VALUE_FUNC:
     {
       Frame_cursor *bottom_bound= get_frame_cursor(thd, spec, false);