[SHOW] EXPLAIN UPDATE/DELETE, code re-structuring

Single table UPDATE/DELETE
- Correctly print type=SIMPLE vs type=PRIMARY
- Handle UPDATE/DELETE of mergeable VIEWs: we get the 
  VIEW's select as the first subquery. 
  (MySQL 5.6 doesn't print it because it finds that the
   subquery is not attached to any select)

mysql-test/r/explain_non_select.result

-drop table if exists t0;
+drop table if exists t0, t1;
 create table t0 (a int) engine=myisam;
 insert into t0 values (1),(2),(3),(4),(5),(6),(7),(8);
 #

sql/opt_qpf.cc

@@ -49,6 +49,7 @@ void QPF_query::add_node(QPF_node *node)
   if (node->get_type() == QPF_node::QPF_UNION)
   {
     QPF_union *u= (QPF_union*)node;
+    DBUG_ASSERT(!unions[u->get_select_id()]);
     unions[u->get_select_id()]= u;
   }
   else
@@ -60,7 +61,10 @@ void QPF_query::add_node(QPF_node *node)
       DBUG_ASSERT(0);
     }
     else
+    {
+      DBUG_ASSERT(!selects[sel->select_id]);
       selects[sel->select_id] = sel;
+    }
   }
 }
 
@@ -493,7 +497,7 @@ int QPF_delete::print_explain(QPF_query *query, select_result_sink *output,
     const char *msg= "Deleting all rows";
     int res= print_explain_message_line(output, explain_flags,
                                         1 /*select number*/,
-                                        "SIMPLE", msg);
+                                        select_type, msg);
     return res;
 
   }
@@ -513,7 +517,7 @@ int QPF_update::print_explain(QPF_query *query, select_result_sink *output,
     const char *msg= "Impossible where";
     int res= print_explain_message_line(output, explain_flags,
                                         1 /*select number*/,
-                                        "SIMPLE", msg);
+                                        select_type, msg);
     return res;
   }
 
@@ -541,7 +545,7 @@ int QPF_update::print_explain(QPF_query *query, select_result_sink *output,
 
   print_explain_row(output, explain_flags, 
                     1, /* id */
-                    "SIMPLE",
+                    select_type,
                     table_name.c_ptr(), 
                     // partitions,
                     jtype,

sql/opt_qpf.h

@@ -350,6 +350,8 @@ public:
   virtual enum qpf_node_type get_type() { return QPF_UPDATE; }
   virtual int get_select_id() { return 1; /* always root */ }
 
+  const char *select_type;
+
   bool impossible_where;
   StringBuffer<64> table_name;
 

sql/sql_delete.cc

@@ -58,10 +58,12 @@ void Delete_plan::save_query_plan_footprint(QPF_query *query)
   if (deleting_all_rows)
   {
     qpf->deleting_all_rows= true;
+    qpf->select_type= "SIMPLE";
   }
   else
   {
-    Update_plan::save_query_plan_footprint_intern(qpf);
+    qpf->deleting_all_rows= false;
+    Update_plan::save_query_plan_footprint_intern(query, qpf);
   }
 
   query->upd_del_plan= qpf;
@@ -71,13 +73,14 @@ void Delete_plan::save_query_plan_footprint(QPF_query *query)
 void Update_plan::save_query_plan_footprint(QPF_query *query)
 {
   QPF_update* qpf= new QPF_update;
-  save_query_plan_footprint_intern(qpf);
+  save_query_plan_footprint_intern(query, qpf);
   query->upd_del_plan= qpf;
 }
 
 
-void Update_plan::save_query_plan_footprint_intern(QPF_update *qpf)
+void Update_plan::save_query_plan_footprint_intern(QPF_query *query, QPF_update *qpf)
 {
+  qpf->select_type= "SIMPLE";
   qpf->table_name.append(table->pos_in_table_list->alias);
   if (impossible_where)
   {
@@ -85,8 +88,10 @@ void Update_plan::save_query_plan_footprint_intern(QPF_update *qpf)
     return;
   }
   
-  // TODO: do we need the following: select_type
-  //select_lex->set_explain_type(TRUE);
+  qpf->impossible_where= false;
+
+  select_lex->set_explain_type(TRUE);
+  qpf->select_type= select_lex->type;
   
   /* Set jtype */
   if (select && select->quick)
@@ -134,6 +139,28 @@ void Update_plan::save_query_plan_footprint_intern(QPF_update *qpf)
   {
     explain_append_mrr_info((QUICK_RANGE_SELECT*)select->quick, &qpf->mrr_type);
   }
+
+  bool skip= updating_a_view;
+  /* Save subquery children */
+  for (SELECT_LEX_UNIT *unit= select_lex->first_inner_unit();
+       unit;
+       unit= unit->next_unit())
+  {
+    if (skip)
+    {
+      skip= false;
+      continue;
+    }
+    /* 
+      Display subqueries only if they are not parts of eliminated WHERE/ON
+      clauses.
+    */
+    if (!(unit->item && unit->item->eliminated))
+      qpf->add_child(unit->first_select()->select_number);
+    
+    //TODO: temporary?:
+    unit->save_qpf(query);
+  }
 }
 
 
@@ -194,6 +221,9 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   query_plan.select_lex= &thd->lex->select_lex;
   query_plan.table= table;
 
+  //psergey-todo: Ugly, discuss with Sanja
+  query_plan.updating_a_view= test(table_list->view);
+
   if (mysql_prepare_delete(thd, table_list, &conds))
     DBUG_RETURN(TRUE);
 
@@ -612,7 +642,7 @@ exit_without_my_ok:
   List<Item> dummy; /* note: looked in 5.6 and they too use a dummy list like this */
   result->prepare(dummy, &thd->lex->unit);
   thd->send_explain_fields(result);
-  int err2= thd->lex->query_plan_footprint->print_explain(result, 0);
+  int err2= thd->lex->query_plan_footprint->print_explain(result, 0 /* explain flags*/);
 
   if (err2)
     result->abort_result_set();

sql/sql_lex.cc

@@ -4337,6 +4337,13 @@ int st_select_lex_unit::save_qpf(QPF_query *output)
 {
   //int res= 0;
   SELECT_LEX *first= first_select();
+
+  if (!first->next_select())
+  {
+    /* This is a 1-way UNION, i.e. not really a UNION */
+    first->save_qpf(output);
+    return 0;
+  }
   
   QPF_union *qpfu= new QPF_union;
   /*

sql/sql_lex.h

@@ -730,10 +730,7 @@ public:
   friend int subselect_union_engine::exec();
 
   List<Item> *get_unit_column_types();
-#if 0  
-  int print_explain(select_result_sink *output, uint8 explain_flags,
-                    bool *printed_anything);
-#endif  
+
   int save_qpf(QPF_query *output);
 };
 
@@ -2379,6 +2376,7 @@ class Update_plan
 protected:
   bool impossible_where;
 public:
+  bool updating_a_view;
   TABLE *table;
   SQL_SELECT *select;
   uint index;
@@ -2396,7 +2394,7 @@ public:
   void set_impossible_where() { impossible_where= true; }
 
   void save_query_plan_footprint(QPF_query *query);
-  void save_query_plan_footprint_intern(QPF_update *qpf);
+  void save_query_plan_footprint_intern(QPF_query *query, QPF_update *qpf);
   virtual ~Update_plan() {}
 
   Update_plan() : impossible_where(false), using_filesort(false) {}

sql/sql_update.cc

@@ -314,6 +314,10 @@ int mysql_update(THD *thd,
     my_error(ER_NON_UPDATABLE_TABLE, MYF(0), table_list->alias, "UPDATE");
     DBUG_RETURN(1);
   }
+  
+  //psergey-todo: Ugly, discuss with Sanja
+  query_plan.updating_a_view= test(table_list->view);
+  
   /* Calculate "table->covering_keys" based on the WHERE */
   table->covering_keys= table->s->keys_in_use;
   table->quick_keys.clear_all();
@@ -1013,13 +1017,14 @@ exit_without_my_ok:
   query_plan.save_query_plan_footprint(thd->lex->query_plan_footprint);
   
   select_send *result;
-  bool printed_anything;
+  //bool printed_anything;
   if (!(result= new select_send()))
     return 1;                               /* purecov: inspected */
   List<Item> dummy; /* note: looked in 5.6 and they too use a dummy list like this */
   result->prepare(dummy, &thd->lex->unit);
   thd->send_explain_fields(result);
-  int err2= thd->lex->print_explain(result, 0 /* explain flags*/, &printed_anything);
+  //int err2= thd->lex->print_explain(result, 0 /* explain flags*/, &printed_anything);
+  int err2= thd->lex->query_plan_footprint->print_explain(result, 0 /* explain flags*/);
 
   if (err2)
     result->abort_result_set();
@@ -1498,6 +1503,7 @@ bool mysql_multi_update(THD *thd,
   {
     if (explain)
     {
+      thd->lex->query_plan_footprint->print_explain(output, 0);
       output->send_eof(); 
       delete output;
     }