MDEV-10059: Compute window functions with same sorting criteria simultaneously

Perform only one table scan for each window function present. We do this
by keeping keeping cursors for each window function frame bound and
running them for each function for every row.

1 files changed, 11 insertions, 32 deletions

diff --git a/sql/item_windowfunc.cc b/sql/item_windowfunc.cc
index d157d545dad..c8ea979900c 100644
--- a/sql/item_windowfunc.cc
+++ b/sql/item_windowfunc.cc
@@ -41,7 +41,7 @@ Item_window_func::resolve_window_name(THD *thd)
     return true;
   }
 
-  return false;                      
+  return false;
 }
 
 
@@ -154,7 +154,7 @@ void Item_window_func::split_sum_func(THD *thd, Ref_ptr_array ref_pointer_array,
 
 
 /*
-  This must be called before advance_window() can be called.
+  This must be called before attempting to compute the window function values.
 
   @detail
     If we attempt to do it in fix_fields(), partition_fields will refer
@@ -162,30 +162,25 @@ void Item_window_func::split_sum_func(THD *thd, Ref_ptr_array ref_pointer_array,
     We need it to refer to temp.table columns.
 */
 
-void Item_window_func::setup_partition_border_check(THD *thd)
-{
-  partition_tracker.init(thd, window_spec->partition_list);
-  window_func()->setup_window_func(thd, window_spec);
-}
-
-
 void Item_sum_rank::setup_window_func(THD *thd, Window_spec *window_spec)
 {
   /* TODO: move this into Item_window_func? */
-  peer_tracker.init(thd, window_spec->order_list);
+  peer_tracker = new Group_bound_tracker(thd, window_spec->order_list);
+  peer_tracker->init();
   clear();
 }
 
 void Item_sum_dense_rank::setup_window_func(THD *thd, Window_spec *window_spec)
 {
   /* TODO: consider moving this && Item_sum_rank's implementation */
-  peer_tracker.init(thd, window_spec->order_list);
+  peer_tracker = new Group_bound_tracker(thd, window_spec->order_list);
+  peer_tracker->init();
   clear();
 }
 
 bool Item_sum_dense_rank::add()
 {
-  if (peer_tracker.check_if_next_group() || first_add)
+  if (peer_tracker->check_if_next_group() || first_add)
   {
     first_add= false;
     dense_rank++;
@@ -198,7 +193,7 @@ bool Item_sum_dense_rank::add()
 bool Item_sum_rank::add()
 {
   row_number++;
-  if (peer_tracker.check_if_next_group())
+  if (peer_tracker->check_if_next_group())
   {
     /* Row value changed */
     cur_rank= row_number;
@@ -206,25 +201,10 @@ bool Item_sum_rank::add()
   return false; 
 }
 
-bool Item_window_func::check_if_partition_changed()
-{
-  return partition_tracker.check_if_next_group();
-}
-
-void Item_window_func::advance_window()
-{
-  if (check_if_partition_changed())
-  {
-    /* Next partition */
-    window_func()->clear();
-  }
-  window_func()->add();
-}
-
 bool Item_sum_percent_rank::add()
 {
   row_number++;
-  if (peer_tracker.check_if_next_group())
+  if (peer_tracker->check_if_next_group())
   {
     /* Row value changed. */
     cur_rank= row_number;
@@ -235,8 +215,7 @@ bool Item_sum_percent_rank::add()
 void Item_sum_percent_rank::setup_window_func(THD *thd, Window_spec *window_spec)
 {
   /* TODO: move this into Item_window_func? */
-  peer_tracker.init(thd, window_spec->order_list);
+  peer_tracker = new Group_bound_tracker(thd, window_spec->order_list);
+  peer_tracker->init();
   clear();
 }
-
-