MDEV-9935: Window functions: assertion failure with empty OVER () clause

Make window functions work with an empty over clause by forcing
a sort on the first column of the current join_tab. This is a temporary
fix until we get window functions to work with big tables.

mysql-test/r/win_empty_over.result

+create table t1 (
+pk int primary key,
+a int,
+b int,
+c char(10),
+d decimal(10, 3),
+e real
+);
+insert into t1 values
+( 1, 0, 1,    'one',    0.1,  0.001),
+( 2, 0, 2,    'two',    0.2,  0.002),
+( 3, 0, 3,    'three',  0.3,  0.003),
+( 4, 1, 2,    'three',  0.4,  0.004),
+( 5, 1, 1,    'two',    0.5,  0.005),
+( 6, 1, 1,    'one',    0.6,  0.006),
+( 7, 2, NULL, 'n_one',  0.5,  0.007),
+( 8, 2, 1,    'n_two',  NULL, 0.008),
+( 9, 2, 2,    NULL,     0.7,  0.009),
+(10, 2, 0,    'n_four', 0.8,  0.010),
+(11, 2, 10,   NULL,     0.9,  NULL);
+select pk, row_number() over () from t1;
+pk	row_number() over ()
+1	1
+2	2
+3	3
+4	4
+5	5
+6	6
+7	7
+8	8
+9	9
+10	10
+11	11
+explain FORMAT=JSON select pk, row_number() over () from t1;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "window_functions_computation": {
+      "sorts": {
+        "filesort": {
+          "sort_key": "pk"
+        }
+      },
+      "temporary_table": {
+        "table": {
+          "table_name": "t1",
+          "access_type": "index",
+          "key": "PRIMARY",
+          "key_length": "4",
+          "used_key_parts": ["pk"],
+          "rows": 11,
+          "filtered": 100,
+          "using_index": true
+        }
+      }
+    }
+  }
+}
+explain FORMAT=JSON select row_number() over (), pk from t1;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "window_functions_computation": {
+      "sorts": {
+        "filesort": {
+          "sort_key": "`row_number() over ()`"
+        }
+      },
+      "temporary_table": {
+        "table": {
+          "table_name": "t1",
+          "access_type": "index",
+          "key": "PRIMARY",
+          "key_length": "4",
+          "used_key_parts": ["pk"],
+          "rows": 11,
+          "filtered": 100,
+          "using_index": true
+        }
+      }
+    }
+  }
+}
+select row_number() over () from (select 4) as t;
+row_number() over ()
+1
+select min(a) over (), max(a) over (), a, row_number() over ()
+from t1
+where a = 0;
+min(a) over ()	max(a) over ()	a	row_number() over ()
+0	0	0	1
+0	0	0	2
+0	0	0	3
+select a, min(a) over (), max(a) over (), row_number() over ()
+from t1
+where a = 0;
+a	min(a) over ()	max(a) over ()	row_number() over ()
+0	0	0	1
+0	0	0	2
+0	0	0	3
+select min(a) over () + 1, max(a) over (), row_number() over ()
+from t1
+where a = 0;
+min(a) over () + 1	max(a) over ()	row_number() over ()
+1	0	1
+1	0	2
+1	0	3
+select min(a) over () + a, max(a) over (), row_number() over ()
+from t1
+where a = 1;
+min(a) over () + a	max(a) over ()	row_number() over ()
+2	1	1
+2	1	2
+2	1	3
+select a + min(a) over (), max(a) over (), row_number() over ()
+from t1
+where a = 1;
+a + min(a) over ()	max(a) over ()	row_number() over ()
+2	1	1
+2	1	2
+2	1	3
+select a + min(a) over () from t1 where a = 1;
+a + min(a) over ()
+2
+2
+2
+create view win_view
+as (select a, min(a) over () from t1 where a = 1);
+select * from win_view;
+a	min(a) over ()
+1	1
+1	1
+1	1
+drop view win_view;
+create view win_view
+as (select a, max(a + 1) over () from t1 where a = 1);
+select * from win_view;
+a	max(a + 1) over ()
+1	3
+1	3
+1	3
+drop view win_view;
+drop table t1;

mysql-test/t/win_empty_over.test

+create table t1 (
+  pk int primary key,
+  a int,
+  b int,
+  c char(10),
+  d decimal(10, 3),
+  e real
+);
+
+insert into t1 values
+( 1, 0, 1,    'one',    0.1,  0.001),
+( 2, 0, 2,    'two',    0.2,  0.002),
+( 3, 0, 3,    'three',  0.3,  0.003),
+( 4, 1, 2,    'three',  0.4,  0.004),
+( 5, 1, 1,    'two',    0.5,  0.005),
+( 6, 1, 1,    'one',    0.6,  0.006),
+( 7, 2, NULL, 'n_one',  0.5,  0.007),
+( 8, 2, 1,    'n_two',  NULL, 0.008),
+( 9, 2, 2,    NULL,     0.7,  0.009),
+(10, 2, 0,    'n_four', 0.8,  0.010),
+(11, 2, 10,   NULL,     0.9,  NULL);
+
+select pk, row_number() over () from t1;
+explain FORMAT=JSON select pk, row_number() over () from t1;
+explain FORMAT=JSON select row_number() over (), pk from t1;
+
+select row_number() over () from (select 4) as t;
+
+--sorted_result
+select min(a) over (), max(a) over (), a, row_number() over ()
+from t1
+where a = 0;
+
+--sorted_result
+select a, min(a) over (), max(a) over (), row_number() over ()
+from t1
+where a = 0;
+
+--sorted_result
+select min(a) over () + 1, max(a) over (), row_number() over ()
+from t1
+where a = 0;
+
+--sorted_result
+select min(a) over () + a, max(a) over (), row_number() over ()
+from t1
+where a = 1;
+
+--sorted_result
+select a + min(a) over (), max(a) over (), row_number() over ()
+from t1
+where a = 1;
+
+select a + min(a) over () from t1 where a = 1;
+
+create view win_view
+as (select a, min(a) over () from t1 where a = 1);
+select * from win_view;
+drop view win_view;
+
+create view win_view
+as (select a, max(a + 1) over () from t1 where a = 1);
+select * from win_view;
+drop view win_view;
+
+drop table t1;

sql/sql_window.cc

@@ -2509,7 +2509,8 @@ bool Window_funcs_sort::exec(JOIN *join)
 
 
 bool Window_funcs_sort::setup(THD *thd, SQL_SELECT *sel,
-                              List_iterator<Item_window_func> &it)
+                              List_iterator<Item_window_func> &it,
+                              JOIN_TAB *join_tab)
 {
   Window_spec *spec;
   Item_window_func *win_func= it.peek();  
@@ -2547,6 +2548,27 @@ bool Window_funcs_sort::setup(THD *thd, SQL_SELECT *sel,
   ORDER* sort_order= concat_order_lists(thd->mem_root, 
                                         spec->partition_list->first,
                                         spec->order_list->first);
+  if (sort_order == NULL) // No partition or order by clause.
+  {
+    /* TODO(cvicentiu) This is used as a way to allow an empty OVER ()
+       clause for window functions. However, a better approach is
+       to not call Filesort at all in this case and just read whatever order
+       the temporary table has.
+       Due to cursors not working for out_of_memory cases (yet!), we have to run
+       filesort to generate a sort buffer of the results.
+       In this case we sort by the first field of the temporary table.
+       We should have this field available, even if it is a window_function
+       field. We don't care of the particular sorting result in this case.
+     */
+    ORDER *order= (ORDER *)alloc_root(thd->mem_root, sizeof(ORDER));
+    memset(order, 0, sizeof(*order));
+    Item *item= new (thd->mem_root) Item_field(thd, join_tab->table->field[0]);
+    order->item= (Item **)alloc_root(thd->mem_root, 2 * sizeof(Item *));
+    order->item[1]= NULL;
+    order->item[0]= item;
+    order->field= join_tab->table->field[0];
+    sort_order= order;
+  }
   filesort= new (thd->mem_root) Filesort(sort_order, HA_POS_ERROR, true, NULL);
 
   /* Apply the same condition that the subsequent sort has. */
@@ -2574,7 +2596,7 @@ bool Window_funcs_computation::setup(THD *thd,
   while (iter.peek())
   {
     if (!(srt= new Window_funcs_sort()) ||
-        srt->setup(thd, sel, iter))
+        srt->setup(thd, sel, iter, tab))
     {
       return true;
     }

sql/sql_window.h

@@ -186,7 +186,8 @@ class Window_func_runner : public Sql_alloc
 class Window_funcs_sort : public Sql_alloc
 {
 public:
-  bool setup(THD *thd, SQL_SELECT *sel, List_iterator<Item_window_func> &it);
+  bool setup(THD *thd, SQL_SELECT *sel, List_iterator<Item_window_func> &it,
+             st_join_table *join_tab);
   bool exec(JOIN *join);
   void cleanup() { delete filesort; }