fixed unlinking SELECT methods

sql/sql_lex.cc

@@ -1112,8 +1112,11 @@ void st_select_lex_unit::exclude_level()
   SELECT_LEX_UNIT *units= 0, **units_last= &units;
   for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
   {
+    // unlink current level from global SELECTs list
     if (sl->link_prev && (*sl->link_prev= sl->link_next))
       sl->link_next->link_prev= sl->link_prev;
+
+    // bring up underlay levels
     SELECT_LEX_UNIT **last= 0;
     for (SELECT_LEX_UNIT *u= sl->first_inner_unit(); u; u= u->next_unit())
     {
@@ -1128,11 +1131,20 @@ void st_select_lex_unit::exclude_level()
   }
   if (units)
   {
+    // include brought up levels in place of current
     (*prev)= units;
     (*units_last)= (SELECT_LEX_UNIT*)next;
+    if (next)
+      next->prev= (SELECT_LEX_NODE**)units_last;
+    units->prev= prev;
   }
   else
+  {
+    // exclude currect unit from list of nodes
     (*prev)= next;
+    if (next)
+      next->prev= prev;
+  }
 }
 
 
@@ -1147,15 +1159,20 @@ void st_select_lex_unit::exclude_tree()
   SELECT_LEX_UNIT *units= 0, **units_last= &units;
   for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
   {
+    // unlink current level from global SELECTs list
     if (sl->link_prev && (*sl->link_prev= sl->link_next))
       sl->link_next->link_prev= sl->link_prev;
 
+    // unlink underlay levels
     for (SELECT_LEX_UNIT *u= sl->first_inner_unit(); u; u= u->next_unit())
     {
       u->exclude_level();
     }
   }
+  // exclude currect unit from list of nodes
   (*prev)= next;
+  if (next)
+    next->prev= prev;
 }