Bug #19814337 - SERVER CRASHES IN ITEM_FUNC_GROUP_CONCAT::FIX_FIELDS ON

		3RD EXECUTION OF PS

Problem:
When order by is by a column number for a group concat function
which has an outer reference, server fails in case of prepared
statements on the third execution

Analysis:
When a group concat function has order by, the fields in order by
are not resolved until execution if the input is a column number.
During execution they get resolved after the temp table gets created.
As a result they will be pointing to temp table fields which are
runtime created objects. This results in dangling pointers leading
to server failure.

Solution:
Reset the pointers for the order by fields to point to the original
arguments after execution as they are invalid.
Done in Item_func_group_concat::cleanup.

sql/item_sum.cc

-/* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.
    rights reserved.
 
    This program is free software; you can redistribute it and/or modify
@@ -3174,6 +3174,19 @@ void Item_func_group_concat::cleanup()
     }
     DBUG_ASSERT(tree == 0);
   }
+  /*
+    As the ORDER structures pointed to by the elements of the
+    'order' array may be modified in find_order_in_list() called
+    from Item_func_group_concat::setup() to point to runtime
+    created objects, we need to reset them back to the original
+    arguments of the function.
+  */
+  ORDER **order_ptr= order;
+  for (uint i= 0; i < arg_count_order; i++)
+  {
+    (*order_ptr)->item= &args[arg_count_field + i];
+    order_ptr++;
+  }
   DBUG_VOID_RETURN;
 }