1 files changed, 37 insertions, 39 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 460b840ef8a..61df2f153db 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -1323,6 +1323,8 @@ void LEX::start(THD *thd_arg)
   frame_bottom_bound= NULL;
   win_spec= NULL;
 
+  upd_del_where= NULL;
+
   vers_conditions.empty();
   period_conditions.empty();
 
@@ -3056,6 +3058,7 @@ void st_select_lex::init_select()
   in_funcs.empty();
   curr_tvc_name= 0;
   versioned_tables= 0;
+  is_tvc_wrapper= false;
   nest_flags= 0;
 }
 
@@ -3980,57 +3983,54 @@ LEX::LEX()
 }
 
 
+bool LEX::can_be_merged()
+{
+  return unit.can_be_merged();
+}
+
+
 /*
-  Check whether the merging algorithm can be used on this VIEW
+  Check whether the merging algorithm can be used for this unit
 
   SYNOPSIS
-    LEX::can_be_merged()
+    st_select_lex_unit::can_be_merged()
 
   DESCRIPTION
-    We can apply merge algorithm if it is single SELECT view  with
-    subqueries only in WHERE clause (we do not count SELECTs of underlying
-    views, and second level subqueries) and we have not grpouping, ordering,
-    HAVING clause, aggregate functions, DISTINCT clause, LIMIT clause and
-    several underlying tables.
+    We can apply merge algorithm for a unit if it is single SELECT with
+    subqueries only in WHERE clauses or in ON conditions or in select list
+    (we do not count SELECTs of underlying  views/derived tables/CTEs and
+    second level subqueries) and we have no grouping, ordering, HAVING
+    clause, aggregate functions, DISTINCT clause, LIMIT clause.
 
   RETURN
     FALSE - only temporary table algorithm can be used
     TRUE  - merge algorithm can be used
 */
 
-bool LEX::can_be_merged()
+bool st_select_lex_unit::can_be_merged()
 {
   // TODO: do not forget implement case when select_lex.table_list.elements==0
 
   /* find non VIEW subqueries/unions */
-  bool selects_allow_merge= (first_select_lex()->next_select() == 0 &&
-                             !(first_select_lex()->uncacheable &
-                               UNCACHEABLE_RAND));
-  if (selects_allow_merge)
-  {
-    for (SELECT_LEX_UNIT *tmp_unit= first_select_lex()->first_inner_unit();
-         tmp_unit;
-         tmp_unit= tmp_unit->next_unit())
-    {
-      if (tmp_unit->first_select()->parent_lex == this &&
-          (tmp_unit->item != 0 &&
-           (tmp_unit->item->place() != IN_WHERE &&
-            tmp_unit->item->place() != IN_ON &&
-            tmp_unit->item->place() != SELECT_LIST)))
-      {
-        selects_allow_merge= 0;
-        break;
-      }
-    }
-  }
-
-  return (selects_allow_merge &&
-          first_select_lex()->group_list.elements == 0 &&
-          first_select_lex()->having == 0 &&
-          first_select_lex()->with_sum_func == 0 &&
-          first_select_lex()->table_list.elements >= 1 &&
-          !(first_select_lex()->options & SELECT_DISTINCT) &&
-          first_select_lex()->limit_params.select_limit == 0);
+  st_select_lex *fs= first_select();
+
+  if (fs->next_select() ||
+      (fs->uncacheable & UNCACHEABLE_RAND) ||
+      (fs->options & SELECT_DISTINCT) ||
+      fs->group_list.elements || fs->having ||
+      fs->with_sum_func ||
+      fs->table_list.elements < 1 ||
+      fs->limit_params.select_limit)
+    return false;
+  for (SELECT_LEX_UNIT *tmp_unit= fs->first_inner_unit();
+       tmp_unit;
+       tmp_unit= tmp_unit->next_unit())
+    if ((tmp_unit->item != 0 &&
+         (tmp_unit->item->place() != IN_WHERE &&
+          tmp_unit->item->place() != IN_ON &&
+          tmp_unit->item->place() != SELECT_LIST)))
+      return false;
+  return true;
 }
 
 
@@ -4105,9 +4105,7 @@ bool LEX::can_not_use_merged(bool no_update_or_delete)
 
   case SQLCOM_UPDATE_MULTI:
   case SQLCOM_DELETE_MULTI:
-    if (no_update_or_delete)
-      return TRUE;
-    /* Fall through */
+    return no_update_or_delete;
 
   default:
     return FALSE;