MDEV-29022 add_slave destroy child list and has dead code

Nowdays subquery in a UNION's ORDER BY placed correctly in fake select,
the only problem was incorrect Name_resolution_contect is fixed by this
patch in parsing, so we do not need scanning/reseting of ORDER BY of
a union.

8 files changed, 10 insertions, 74 deletions

diff --git a/sql/item.h b/sql/item.h
index b16456372d4..f28e4fb4bd7 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1758,7 +1758,6 @@ public:
   virtual bool enumerate_field_refs_processor(void *arg) { return 0; }
   virtual bool mark_as_eliminated_processor(void *arg) { return 0; }
   virtual bool eliminate_subselect_processor(void *arg) { return 0; }
-  virtual bool set_fake_select_as_master_processor(void *arg) { return 0; }
   virtual bool view_used_tables_processor(void *arg) { return 0; }
   virtual bool eval_not_null_tables(void *arg) { return 0; }
   virtual bool is_subquery_processor(void *arg) { return 0; }
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index ee36ee2fae9..6472bb86a37 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -386,50 +386,6 @@ bool Item_subselect::eliminate_subselect_processor(void *arg)
 }
 
 
-/**
-  Adjust the master select of the subquery to be the fake_select which
-  represents the whole UNION right above the subquery, instead of the
-  last query of the UNION.
-
-  @param arg  pointer to the fake select
-
-  @return
-    FALSE to force the evaluation of the processor for the subsequent items.
-*/
-
-bool Item_subselect::set_fake_select_as_master_processor(void *arg)
-{
-  SELECT_LEX *fake_select= (SELECT_LEX*) arg;
-  /*
-    Move the st_select_lex_unit of a subquery from a global ORDER BY clause to
-    become a direct child of the fake_select of a UNION. In this way the
-    ORDER BY that is applied to the temporary table that contains the result of
-    the whole UNION, and all columns in the subquery are resolved against this
-    table. The transformation is applied only for immediate child subqueries of
-    a UNION query.
-  */
-  if (unit->outer_select()->master_unit()->fake_select_lex == fake_select)
-  {
-    /*
-      Set the master of the subquery to be the fake select (i.e. the whole
-      UNION), instead of the last query in the UNION.
-    */
-    fake_select->add_slave(unit);
-    DBUG_ASSERT(unit->outer_select() == fake_select);
-    /* Adjust the name resolution context hierarchy accordingly. */
-    for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
-      sl->context.outer_context= &(fake_select->context);
-    /*
-      Undo Item_subselect::eliminate_subselect_processor because at that phase
-      we don't know yet that the ORDER clause will be moved to the fake select.
-    */
-    unit->item= this;
-    eliminated= FALSE;
-  }
-  return FALSE;
-}
-
-
 bool Item_subselect::mark_as_dependent(THD *thd, st_select_lex *select, 
                                        Item *item)
 {
diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 16c683b27e0..b95a02d28b2 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -238,7 +238,6 @@ public:
   bool walk(Item_processor processor, bool walk_subquery, void *arg);
   bool mark_as_eliminated_processor(void *arg);
   bool eliminate_subselect_processor(void *arg);
-  bool set_fake_select_as_master_processor(void *arg);
   bool enumerate_field_refs_processor(void *arg);
   bool check_vcol_func_processor(void *arg) 
   {
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 3400e31fd5c..c5bdfb596eb 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -2434,23 +2434,9 @@ void st_select_lex_node::include_down(st_select_lex_node *upper)
 }
 
 
-void st_select_lex_node::add_slave(st_select_lex_node *slave_arg)
+void st_select_lex_node::attach_single(st_select_lex_node *slave_arg)
 {
-  for (; slave; slave= slave->next)
-    if (slave == slave_arg)
-      return;
-
-  if (slave)
-  {
-    st_select_lex_node *slave_arg_slave= slave_arg->slave;
-    /* Insert in the front of list of slaves if any. */
-    slave_arg->include_neighbour(slave);
-    /* include_neighbour() sets slave_arg->slave=0, restore it. */
-    slave_arg->slave= slave_arg_slave;
-    /* Count on include_neighbour() setting the master. */
-    DBUG_ASSERT(slave_arg->master == this);
-  }
-  else
+  DBUG_ASSERT(slave == 0);
   {
     slave= slave_arg;
     slave_arg->master= this;
diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index d720d902bd7..bdc8b5476b2 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -705,7 +705,7 @@ public:
 
   inline st_select_lex_node* get_master() { return master; }
   void include_down(st_select_lex_node *upper);
-  void add_slave(st_select_lex_node *slave_arg);
+  void attach_single(st_select_lex_node *slave_arg);
   void include_neighbour(st_select_lex_node *before);
   void include_standalone(st_select_lex_node *sel, st_select_lex_node **ref);
   void include_global(st_select_lex_node **plink);
diff --git a/sql/sql_tvc.cc b/sql/sql_tvc.cc
index 13efd973326..43c25db5097 100644
--- a/sql/sql_tvc.cc
+++ b/sql/sql_tvc.cc
@@ -708,7 +708,7 @@ st_select_lex *wrap_tvc(THD *thd, st_select_lex *tvc_sl,
     Attach the select used of TVC as the only slave to the unit for
     the derived table tvc_x of the transformation
   */
-  derived_unit->add_slave(tvc_sl);
+  derived_unit->attach_single(tvc_sl);
   tvc_sl->linkage= DERIVED_TABLE_TYPE;
 
   /*
diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 32d307de5e8..e831e2a479c 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -633,15 +633,6 @@ st_select_lex_unit::init_prepare_fake_select_lex(THD *thd_arg,
          order= order->next)
       order->item= &order->item_ptr;
   }
-  for (ORDER *order= global_parameters()->order_list.first;
-       order;
-       order=order->next)
-  {
-    (*order->item)->walk(&Item::change_context_processor, 0,
-                         &fake_select_lex->context);
-    (*order->item)->walk(&Item::set_fake_select_as_master_processor, 0,
-                         fake_select_lex);
-  }
 }
 
 
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 577405725ca..d89ef534486 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -12910,11 +12910,16 @@ order_clause:
                */
                DBUG_ASSERT(sel->master_unit()->fake_select_lex);
                lex->current_select= sel->master_unit()->fake_select_lex;
+               lex->push_context(&sel->master_unit()->fake_select_lex->context, thd->mem_root);
              }
           }
           order_list
           {
-
+            if (Lex->current_select ==
+                Lex->current_select->master_unit()->fake_select_lex)
+            {
+              Lex->pop_context();
+            }
           }
          ;