Merge from mysql-5.1.

1 files changed, 37 insertions, 10 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 952d1b83ce6..22913c75d48 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -647,8 +647,11 @@ JOIN::prepare(Item ***rref_pointer_array,
   this->group= group_list != 0;
   unit= unit_arg;
 
+  if (tmp_table_param.sum_func_count && !group_list)
+    implicit_grouping= TRUE;
+
 #ifdef RESTRICTED_GROUP
-  if (sum_func_count && !group_list && (func_count || field_count))
+  if (implicit_grouping)
   {
     my_message(ER_WRONG_SUM_SELECT,ER(ER_WRONG_SUM_SELECT),MYF(0));
     goto err;
@@ -884,15 +887,23 @@ JOIN::optimize()
   }
 #endif
 
-  /* Optimize count(*), min() and max() */
-  if (tables_list && tmp_table_param.sum_func_count && ! group_list)
+  /* 
+     Try to optimize count(*), min() and max() to const fields if
+     there is implicit grouping (aggregate functions but no
+     group_list). In this case, the result set shall only contain one
+     row. 
+  */
+  if (tables_list && implicit_grouping)
   {
     int res;
     /*
       opt_sum_query() returns HA_ERR_KEY_NOT_FOUND if no rows match
       to the WHERE conditions,
-      or 1 if all items were resolved,
+      or 1 if all items were resolved (optimized away),
       or 0, or an error number HA_ERR_...
+
+      If all items were resolved by opt_sum_query, there is no need to
+      open any tables.
     */
     if ((res=opt_sum_query(select_lex->leaf_tables, all_fields, conds)))
     {
@@ -1234,13 +1245,22 @@ JOIN::optimize()
       (!group_list && tmp_table_param.sum_func_count))
     order=0;
 
-  // Can't use sort on head table if using row cache
+  // Can't use sort on head table if using join buffering
   if (full_join)
   {
-    if (group_list)
-      simple_group=0;
-    if (order)
-      simple_order=0;
+    TABLE *stable= (sort_by_table == (TABLE *) 1 ? 
+      join_tab[const_tables].table : sort_by_table);
+    /* 
+      FORCE INDEX FOR ORDER BY can be used to prevent join buffering when
+      sorting on the first table.
+    */
+    if (!stable || !stable->force_index_order)
+    {
+      if (group_list)
+        simple_group= 0;
+      if (order)
+        simple_order= 0;
+    }
   }
 
   /*
@@ -2018,7 +2038,8 @@ JOIN::exec()
     count_field_types(select_lex, &curr_join->tmp_table_param, 
                       *curr_all_fields, 0);
   
-  if (curr_join->group || curr_join->tmp_table_param.sum_func_count ||
+  if (curr_join->group || curr_join->implicit_grouping ||
+      curr_join->tmp_table_param.sum_func_count ||
       (procedure && (procedure->flags & PROC_GROUP)))
   {
     if (make_group_fields(this, curr_join))
@@ -10805,6 +10826,12 @@ Next_select_func setup_end_select_func(JOIN *join)
   }
   else
   {
+    /* 
+       Choose method for presenting result to user. Use end_send_group
+       if the query requires grouping (has a GROUP BY clause and/or one or
+       more aggregate functions). Use end_send if the query should not
+       be grouped.
+     */
     if ((join->sort_and_group ||
          (join->procedure && join->procedure->flags & PROC_GROUP)) &&
         !tmp_tbl->precomputed_group_by)