MDEV-10879: Window Functions final ordering of result setbb-10.2-vicentiu3

Window functions now force an ordering to the result set if none is
specified through order by. The ordering that will be returned is the final ordering
that is used during window function computation. For multiple window functions,
it should generally be the most specific sort ordering for the final
window function in the select list.

1 files changed, 25 insertions, 6 deletions

diff --git a/sql/sql_window.cc b/sql/sql_window.cc
index 0e407308d4e..518e469a194 100644
--- a/sql/sql_window.cc
+++ b/sql/sql_window.cc
@@ -2758,7 +2758,7 @@ bool Window_func_runner::exec(THD *thd, TABLE *tbl, SORT_INFO *filesort_result)
 }
 
 
-bool Window_funcs_sort::exec(JOIN *join)
+bool Window_funcs_sort::exec(JOIN *join, bool keep_filesort_result)
 {
   THD *thd= join->thd;
   JOIN_TAB *join_tab= join->join_tab + join->exec_join_tab_cnt();
@@ -2773,8 +2773,20 @@ bool Window_funcs_sort::exec(JOIN *join)
 
   bool is_error= runner.exec(thd, tbl, filesort_result);
 
-  delete join_tab->filesort_result;
-  join_tab->filesort_result= NULL;
+  /*
+     During create_sort_index, we set the filesort_result field within the
+     join_tab. We will reuse the sorting if we don't have an additional
+     ORDER BY clause for our table in the select statement encompasing these
+     window functions. We only keep the last Window_funcs_sort filesort result.
+
+     Free the filesort_result if we encountered an error during execution so as
+     to prevent memory leaks.
+  */
+  if (!keep_filesort_result || is_error)
+  {
+    delete join_tab->filesort_result;
+    join_tab->filesort_result= NULL;
+  }
   return is_error;
 }
 
@@ -2883,14 +2895,21 @@ bool Window_funcs_computation::setup(THD *thd,
 }
 
 
-bool Window_funcs_computation::exec(JOIN *join)
+bool Window_funcs_computation::exec(JOIN *join, bool keep_final_sort_result)
 {
   List_iterator<Window_funcs_sort> it(win_func_sorts);
+  uint count= 0;
   Window_funcs_sort *srt;
   /* Execute each sort */
-  while ((srt = it++))
+  bool keep_result= false;
+  while ((srt= it++))
   {
-    if (srt->exec(join))
+    count++;
+    /* The final Window_funcs_sort keeps the filesort result. */
+    if (keep_final_sort_result && count == win_func_sorts.elements)
+      keep_result= true;
+
+    if (srt->exec(join, keep_result))
       return true;
   }
   return false;