Bug #13444084:PRIMARY KEY OR UNIQUE KEY >453 BYTES FAILS FOR

              COUNT DISTINCT GROUP BY

PROBLEM:
To calculate the final result of the count(distinct(select 1))
we call 'end_send' function instead of 'end_send_group'.
'end_send' cannot be called if we have aggregate functions
that need to be evaluated.

ANALYSIS:
While evaluating for a possible loose_index_scan option for
the query, the variable 'is_agg_distinct' is set to 'false'
as the item in the distinct clause is not a field. But, we
choose loose_index_scan by not taking this into 
consideration.
So, while setting the final 'select_function' to evaluate
the result, 'precomputed_group_by' is set to TRUE as in
this case loose_index_scan is chosen and we do not have
agg_distinct in the query (which is clearly wrong as we
have one).
As a result, 'end_send' function is chosen as the final
select_function instead of 'end_send_group'. The difference
between the two being, 'end_send_group' evaluates the
aggregates while 'end_send' does not. Hence the wrong result.

FIX:
The variable 'is_agg_distinct' always represents if 
'loose_idnex_scan' can be chosen for aggregate_distinct 
functions present in the select.
So, we check for this variable to continue with 
loose_index_scan option.


sql/opt_range.cc:
  Do not continue if is_agg_distinct is not set in case
  of agg_distinct functions.

sql/opt_range.cc

@@ -9463,9 +9463,10 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
         have_min= TRUE;
       else if (min_max_item->sum_func() == Item_sum::MAX_FUNC)
         have_max= TRUE;
-      else if (min_max_item->sum_func() == Item_sum::COUNT_DISTINCT_FUNC ||
+      else if (is_agg_distinct &&
+               (min_max_item->sum_func() == Item_sum::COUNT_DISTINCT_FUNC ||
                 min_max_item->sum_func() == Item_sum::SUM_DISTINCT_FUNC ||
-               min_max_item->sum_func() == Item_sum::AVG_DISTINCT_FUNC)
+                min_max_item->sum_func() == Item_sum::AVG_DISTINCT_FUNC))
         continue;
       else
         DBUG_RETURN(NULL);