Merge bk-internal.mysql.com:/home/bk/mysql-5.0

into mysql.com:/opt/local/work/mysql-5.0-7306-new


sql/item_subselect.cc:
  Auto merged
sql/mysql_priv.h:
  Auto merged
sql/opt_range.cc:
  Auto merged
sql/sql_base.cc:
  Auto merged
sql/sql_insert.cc:
  Auto merged
sql/sql_lex.cc:
  Auto merged
sql/sql_lex.h:
  Auto merged
sql/sql_olap.cc:
  Auto merged
sql/sql_parse.cc:
  Auto merged
sql/sql_select.cc:
  Auto merged

1 files changed, 10 insertions, 1 deletions

diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 5718ab5e010..c250238eb4b 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -7980,8 +7980,17 @@ void QUICK_GROUP_MIN_MAX_SELECT::update_key_stat()
       }
     }
   }
-  else if (have_min && min_max_arg_part && min_max_arg_part->field->is_null())
+  else if (have_min && min_max_arg_part &&
+           min_max_arg_part->field->real_maybe_null())
   {
+    /*
+      If a MIN/MAX argument value is NULL, we can quickly determine
+      that we're in the beginning of the next group, because NULLs
+      are always < any other value. This allows us to quickly
+      determine the end of the current group and jump to the next
+      group (see next_min()) and thus effectively increases the
+      usable key length.
+    */
     max_used_key_length+= min_max_arg_len;
     ++used_key_parts;
   }