Patch for Bug#13805127: Stored program cache produces wrong result in same THD.

Background:

  - as described in MySQL Internals Prepared Stored
    (http://forge.mysql.com/wiki/MySQL_Internals_Prepared_Stored),
    the Optimizer sometimes does destructive changes to the parsed
    LEX-object (Item-tree), which makes it impossible to re-use
    that tree for PS/SP re-execution.

  - in order to be able to re-use the Item-tree, the destructive
    changes are remembered and rolled back after the statement execution.

The problem, discovered by this bug, was that the objects representing
GROUP-BY clause did not restored after query execution. So, the GROUP-BY
part of the statement could not be properly re-initialized for re-execution
after destructive changes.

Those objects do not take part in the Item-tree, so they can not be saved
using the approach for Item-tree.

The fix is as follows:

  - introduce a new array in st_select_lex to store the original
    ORDER pointers, representing the GROUP-BY clause;

  - Initialize this array in fix_prepare_information().

  - restore the list of GROUP-BY items in reinit_stmt_before_use().

1 files changed, 8 insertions, 0 deletions

diff --git a/sql/sql_prepare.cc b/sql/sql_prepare.cc
index 8390594c2eb..d0bfecebc82 100644
--- a/sql/sql_prepare.cc
+++ b/sql/sql_prepare.cc
@@ -2422,6 +2422,14 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
       DBUG_ASSERT(sl->join == 0);
       ORDER *order;
       /* Fix GROUP list */
+      if (sl->group_list_ptrs && sl->group_list_ptrs->size() > 0)
+      {
+        for (uint ix= 0; ix < sl->group_list_ptrs->size() - 1; ++ix)
+        {
+          order= sl->group_list_ptrs->at(ix);
+          order->next= sl->group_list_ptrs->at(ix+1);
+        }
+      }
       for (order= sl->group_list.first; order; order= order->next)
         order->item= &order->item_ptr;
       /* Fix ORDER list */