It is now possible to remove values multiple times from window functions

This can happen with degenerate frame definitions that are always empty.

mysql-test/r/win.result

@@ -1189,6 +1189,44 @@ pk	c	cnt
 10	2	0
 select
 pk, c,
+sum(c) over (partition by c
+order by pk
+rows between 1 preceding
+and 2 preceding)
+as sum
+from t1;
+pk	c	sum
+1	1	NULL
+2	1	NULL
+3	1	NULL
+4	1	NULL
+5	2	NULL
+6	2	NULL
+7	2	NULL
+8	2	NULL
+9	2	NULL
+10	2	NULL
+select
+pk, c,
+sum(c) over (partition by c
+order by pk
+rows between 2 following
+and 1 following)
+as sum
+from t1;
+pk	c	sum
+1	1	NULL
+2	1	NULL
+3	1	NULL
+4	1	NULL
+5	2	NULL
+6	2	NULL
+7	2	NULL
+8	2	NULL
+9	2	NULL
+10	2	NULL
+select
+pk, c,
 count(*) over (partition by c
 order by pk
 range between 1 preceding
@@ -1788,15 +1826,12 @@ rank() over (order by b)
 0
 0
 drop table t1;
-#
-# MDEV-9894: Assertion `0' failed in Window_func_runner::setup
-#  return ER_NOT_SUPPORTED_YET for aggregates that are not yet supported
-#  as window functions.
-#
 create table t1 (i int);
 insert into t1 values (1),(2);
 SELECT MAX(i) OVER (PARTITION BY (i)) FROM t1;
-ERROR 42000: This version of MariaDB doesn't yet support 'This aggregate as window function'
+MAX(i) OVER (PARTITION BY (i))
+1
+2
 drop table t1;
 #
 # Check the 0 in ROWS 0 PRECEDING

mysql-test/t/win.test

@@ -745,6 +745,24 @@ select
                 as cnt
 from t1;
 
+select
+  pk, c,
+  sum(c) over (partition by c
+                 order by pk
+                 rows between 1 preceding
+                          and 2 preceding)
+                as sum
+from t1;
+
+select
+  pk, c,
+  sum(c) over (partition by c
+                 order by pk
+                 rows between 2 following
+                          and 1 following)
+                as sum
+from t1;
+
 
 select
   pk, c,
@@ -1089,14 +1107,8 @@ from
 
 drop table t1;
 
---echo #
---echo # MDEV-9894: Assertion `0' failed in Window_func_runner::setup
---echo #  return ER_NOT_SUPPORTED_YET for aggregates that are not yet supported
---echo #  as window functions.
---echo #
 create table t1 (i int);
 insert into t1 values (1),(2);
---error ER_NOT_SUPPORTED_YET
 SELECT MAX(i) OVER (PARTITION BY (i)) FROM t1;
 drop table t1;
 

sql/item_sum.cc

@@ -1352,11 +1352,15 @@ void Item_sum_sum::add_helper(bool perform_removal)
     {
       if (perform_removal)
       {
-        DBUG_ASSERT(count > 0);
+        if (count > 0)
+        {
           my_decimal_sub(E_DEC_FATAL_ERROR, dec_buffs + (curr_dec_buff ^ 1),
                          dec_buffs + curr_dec_buff, val);
           count--;
         }
+        else
+          DBUG_VOID_RETURN;
+      }
       else
       {
         count++;
@@ -1369,7 +1373,7 @@ void Item_sum_sum::add_helper(bool perform_removal)
   }
   else
   {
-    if (perform_removal)
+    if (perform_removal && count > 0)
       sum-= aggr->arg_val_real();
     else
       sum+= aggr->arg_val_real();
@@ -1377,9 +1381,11 @@ void Item_sum_sum::add_helper(bool perform_removal)
     {
       if (perform_removal)
       {
-        DBUG_ASSERT(count > 0);
+        if (count > 0)
+        {
           count--;
         }
+      }
       else
         count++;
 
@@ -1598,6 +1604,7 @@ void Item_sum_count::remove()
   DBUG_ASSERT(aggr->Aggrtype() == Aggregator::SIMPLE_AGGREGATOR);
   if (aggr->arg_is_null(false))
     return;
+  if (count > 0)
     count--;
 }
 
@@ -1702,7 +1709,7 @@ void Item_sum_avg::remove()
   Item_sum_sum::remove();
   if (!aggr->arg_is_null(true))
   {
-    DBUG_ASSERT(count > 0);
+    if (count > 0)
       count--;
   }
 }
@@ -2190,6 +2197,9 @@ bool Item_sum_bit::clear_as_window()
 bool Item_sum_bit::remove_as_window(ulonglong value)
 {
   DBUG_ASSERT(as_window_function);
+  if (num_values_added == 0)
+    return 0; // Nothing to remove.
+
   for (int i= 0; i < NUM_BIT_COUNTERS; i++)
   {
     if (!bit_counters[i])
@@ -2200,7 +2210,7 @@ bool Item_sum_bit::remove_as_window(ulonglong value)
     }
     bit_counters[i]-= (value & (1 << i)) ? 1 : 0;
   }
-  DBUG_ASSERT(num_values_added > 0);
+
   // Prevent overflow;
   num_values_added = std::min(num_values_added, num_values_added - 1);
   set_bits_from_counters();