Window functions: make "ORDER BY window_func" work

- When window functions are present, JOIN::simple_order should be set
  to FALSE. (Otherwise, the optimizer may attempt to do a "pre-sorting"
  on the first join_tab. Which can work in some cases, but generally
  isn't)

- filesort tries to only read table fields that it requires. Window
  function requires its temp.table field.  In order to pass this info
  to filesort, added an implementation of Item_window_func::
  register_field_in_read_map.

1 files changed, 19 insertions, 0 deletions

diff --git a/sql/item_windowfunc.h b/sql/item_windowfunc.h
index f239f7f2ccf..ad72bd7040c 100644
--- a/sql/item_windowfunc.h
+++ b/sql/item_windowfunc.h
@@ -511,6 +511,25 @@ public:
 
   void update_used_tables();
 
+  /*
+    This is used by filesort to mark the columns it needs to read (because they
+    participate in the sort criteria and/or row retrieval. Window functions can
+    only be used in sort criteria).
+
+    Sorting by window function value is only done after the window functions
+    have been computed. In that case, window function will need to read its
+    temp.table field. In order to allow that, mark that field in the read_set.
+  */
+  bool register_field_in_read_map(uchar *arg)
+  {
+    TABLE *table= (TABLE*) arg;
+    if (result_field && (result_field->table == table || !table))
+    {
+      bitmap_set_bit(result_field->table->read_set, result_field->field_index);
+    }
+    return 0;
+  }
+
   bool is_frame_prohibited() const
   {
     switch (window_func()->sum_func()) {