Fix for bug#49897: crash in ptr_compare when char(0) NOT NULL

column is used for ORDER BY

Problem: filesort isn't meant for null length sort data
(e.g. char(0)), that leads to a server crash.

Fix: disregard sort order if sort data record length is 0 (nothing
to sort).


mysql-test/r/select.result:
  Fix for bug#49897: crash in ptr_compare when char(0) NOT NULL 
  column is used for ORDER BY
    - test result.
mysql-test/t/select.test:
  Fix for bug#49897: crash in ptr_compare when char(0) NOT NULL 
  column is used for ORDER BY
    - test case.
sql/filesort.cc:
  Fix for bug#49897: crash in ptr_compare when char(0) NOT NULL 
  column is used for ORDER BY
    - assert added as filesort cannot handle null length sort data.
sql/sql_select.cc:
  Fix for bug#49897: crash in ptr_compare when char(0) NOT NULL 
  column is used for ORDER BY
    - don't sort null length data e.g. in case of ORDER BY CHAR(0).

1 files changed, 13 insertions, 0 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index d8ec5eff5c1..239809f1d4c 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -521,13 +521,26 @@ JOIN::prepare(Item ***rref_pointer_array,
 
   if (order)
   {
+    bool real_order= FALSE;
     ORDER *ord;
     for (ord= order; ord; ord= ord->next)
     {
       Item *item= *ord->item;
+      /*
+        Disregard sort order if there's only "{VAR}CHAR(0) NOT NULL" fields
+        there. Such fields don't contain any data to sort.
+      */
+      if (!real_order &&
+          (item->type() != Item::Item::FIELD_ITEM ||
+           ((Item_field *) item)->field->maybe_null() ||
+           ((Item_field *) item)->field->sort_length()))
+        real_order= TRUE;
+
       if (item->with_sum_func && item->type() != Item::SUM_FUNC_ITEM)
         item->split_sum_func(thd, ref_pointer_array, all_fields);
     }
+    if (!real_order)
+      order= NULL;
   }
 
   if (having && having->with_sum_func)