Optimisation if simple IN subselect with primary index

(SCRUM) (part of WL#818)

mysql-test/r/subselect.result

@@ -1226,7 +1226,15 @@ a
 explain select * from t2 where t2.a in (select a from t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	index	NULL	PRIMARY	4	NULL	4	Using where; Using index
-2	DEPENDENT SUBQUERY	t1	eq_ref	PRIMARY	PRIMARY	4	func	1	Using where; Using index
+2	DEPENDENT SUBQUERY	t1	simple_in	PRIMARY	PRIMARY	4	func	1	Using index
+select * from t2 where t2.a in (select a from t1 where t1.b <> 30);
+a
+2
+4
+explain select * from t2 where t2.a in (select a from t1 where t1.b <> 30);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	NULL	PRIMARY	4	NULL	4	Using where; Using index
+2	DEPENDENT SUBQUERY	t1	simple_in	PRIMARY	PRIMARY	4	func	1	Using index; Using where
 select * from t2 where t2.a in (select t1.a from t1,t3 where t1.b=t3.a);
 a
 2

mysql-test/t/subselect.test

@@ -819,6 +819,8 @@ insert into t2 values (2), (3), (4), (5);
 insert into t3 values (10,3), (20,4), (30,5);
 select * from t2 where t2.a in (select a from t1);
 explain select * from t2 where t2.a in (select a from t1);
+select * from t2 where t2.a in (select a from t1 where t1.b <> 30);
+explain select * from t2 where t2.a in (select a from t1 where t1.b <> 30);
 select * from t2 where t2.a in (select t1.a from t1,t3 where t1.b=t3.a);
 explain select * from t2 where t2.a in (select t1.a from t1,t3 where t1.b=t3.a);
 drop table t1, t2, t3;

sql/item_subselect.cc

@@ -36,7 +36,7 @@ inline Item * and_items(Item* cond, Item *item)
 
 Item_subselect::Item_subselect():
   Item_result_field(), engine_owner(1), value_assigned(0), substitution(0),
-  have_to_be_excluded(0)
+  have_to_be_excluded(0), engine_changed(0)
 {
   reset();
   /*
@@ -117,16 +117,22 @@ bool Item_subselect::fix_fields(THD *thd_param, TABLE_LIST *tables, Item **ref)
 
 bool Item_subselect::exec()
 {
+  int res;
   MEM_ROOT *old_root= my_pthread_getspecific_ptr(MEM_ROOT*, THR_MALLOC);
   if (&thd->mem_root != old_root)
   {
     my_pthread_setspecific_ptr(THR_MALLOC, &thd->mem_root);
-    int res= engine->exec();
+    res= engine->exec();
     my_pthread_setspecific_ptr(THR_MALLOC, old_root);
-    return (res);
   }
   else
-    return engine->exec();
+    res= engine->exec();
+  if (engine_changed)
+  {
+    engine_changed= 0;
+    return exec();
+  }
+  return (res);
 }
 
 Item::Type Item_subselect::type() const 
@@ -795,6 +801,13 @@ int subselect_union_engine::prepare()
   return unit->prepare(thd, result, 0);
 }
 
+int subselect_simplein_engine::prepare()
+{
+  //this never should be called
+  DBUG_ASSERT(0);
+  return 1;
+}
+
 static Item_result set_row(SELECT_LEX *select_lex, Item * item,
 			   Item_cache **row, bool *maybe_null)
 {
@@ -873,6 +886,12 @@ void subselect_union_engine::fix_length_and_dec(Item_cache **row)
   }
 }
 
+void subselect_simplein_engine::fix_length_and_dec(Item_cache **row)
+{
+  //this never should be called
+  DBUG_ASSERT(0);
+}
+
 int subselect_single_select_engine::exec()
 {
   DBUG_ENTER("subselect_single_select_engine::exec");
@@ -889,6 +908,10 @@ int subselect_single_select_engine::exec()
       join->thd->lex.current_select= save_select;
       DBUG_RETURN(join->error?join->error:1);
     }
+    if (item->engine_changed)
+    {
+      DBUG_RETURN(1);
+    }
   }
   if ((select_lex->dependent || select_lex->uncacheable) && executed)
   {
@@ -922,6 +945,51 @@ int subselect_union_engine::exec()
   return res;
 }
 
+int subselect_simplein_engine::exec()
+{
+  DBUG_ENTER("subselect_simplein_engine::exec");
+  int error;
+  TABLE *table= tab->table;
+  if ((tab->ref.key_err= (*tab->ref.key_copy)->copy()))
+  {
+    table->status= STATUS_NOT_FOUND;
+    error= -1;
+  }
+  else
+  {
+    error= table->file->index_read(table->record[0],
+				   tab->ref.key_buff,
+				   tab->ref.key_length,HA_READ_KEY_EXACT);
+    if (error && error != HA_ERR_KEY_NOT_FOUND)
+      error= report_error(table, error);
+    else
+    {
+      error= 0;
+      table->null_row= 0;
+      if (table->status)
+	((Item_in_subselect *) item)->value= 0;
+      else
+	((Item_in_subselect *) item)->value= (!cond || cond->val_int()?1:0);
+    }
+  }
+  {
+    int tmp= 0;
+    if ((tmp= table->file->extra(HA_EXTRA_NO_CACHE)))
+    {
+      DBUG_PRINT("error", ("extra(HA_EXTRA_NO_CACHE) failed"));
+      error= 1;
+    }
+    if ((tmp= table->file->index_end()))
+    {
+      DBUG_PRINT("error", ("index_end() failed"));
+      error= 1;
+    }
+    if (error == 1)
+      table->file->print_error(tmp, MYF(0));
+  }
+  DBUG_RETURN(error != 0)
+}
+
 uint subselect_single_select_engine::cols()
 {
   return select_lex->item_list.elements;
@@ -961,3 +1029,9 @@ void subselect_union_engine::exclude()
 {
   unit->exclude_level();
 }
+
+void subselect_simplein_engine::exclude()
+{
+  //this never should be called
+  DBUG_ASSERT(0);
+}

sql/item_subselect.h

@@ -48,7 +48,12 @@ class Item_subselect :public Item_result_field
   bool have_to_be_excluded;
 
 public:
+  /* changed engine indicator */
+  bool engine_changed;
+
   enum trans_res {OK, REDUCE, ERROR};
+  enum subs_type {UNKNOWN_SUBS, SINGLEROW_SUBS,
+		  EXISTS_SUBS, IN_SUBS, ALLANY_SUBS};
 
   Item_subselect();
   Item_subselect(Item_subselect *item)
@@ -59,9 +64,12 @@ class Item_subselect :public Item_result_field
     max_columns= item->max_columns;
     engine= item->engine;
     engine_owner= 0;
+    engine_changed= item->engine_changed;
     name= item->name;
   }
 
+  virtual subs_type substype() { return UNKNOWN_SUBS; }
+
   /* 
      We need this method, because some compilers do not allow 'this'
      pointer in constructor initialization list, but we need pass pointer
@@ -95,6 +103,12 @@ class Item_subselect :public Item_result_field
     else
       str->append("-subselect-");
   }
+  bool change_engine(subselect_engine *eng)
+  {
+    engine= eng;
+    engine_changed= 1;
+    return eng == 0;
+  }
 
   friend class select_subselect;
   friend class Item_in_optimizer;
@@ -116,6 +130,9 @@ class Item_singlerow_subselect :public Item_subselect
     max_length= item->max_length;
     decimals= item->decimals;
   }
+
+  subs_type substype() { return SINGLEROW_SUBS; }
+
   void reset();
   trans_res select_transformer(JOIN *join);
   void store(uint i, Item* item);
@@ -152,6 +169,7 @@ class Item_exists_subselect :public Item_subselect
   }
   Item_exists_subselect(): Item_subselect() {}
 
+  subs_type substype() { return EXISTS_SUBS; }
   void reset() 
   {
     value= 0;
@@ -165,6 +183,7 @@ class Item_exists_subselect :public Item_subselect
   void fix_length_and_dec();
 
   friend class select_exists_subselect;
+  friend class subselect_simplein_engine;
 };
 
 /* IN subselect */
@@ -185,6 +204,8 @@ class Item_in_subselect :public Item_exists_subselect
   Item_in_subselect(THD *thd, Item * left_expr, st_select_lex *select_lex);
   Item_in_subselect(Item_in_subselect *item);
   Item_in_subselect(): Item_exists_subselect(),  abort_on_null(0)  {}
+
+  subs_type substype() { return IN_SUBS; }
   void reset() 
   {
     value= 0;
@@ -218,6 +239,7 @@ class Item_allany_subselect :public Item_in_subselect
   Item_allany_subselect(THD *thd, Item * left_expr, compare_func_creator f,
 		     st_select_lex *select_lex);
   Item_allany_subselect(Item_allany_subselect *item);
+  subs_type substype() { return ALLANY_SUBS; }
   trans_res select_transformer(JOIN *join);
 };
 
@@ -288,3 +310,24 @@ class subselect_union_engine: public subselect_engine
   bool uncacheable();
   void exclude();
 };
+
+struct st_join_table;
+class subselect_simplein_engine: public subselect_engine
+{
+  st_join_table *tab;
+  Item *cond;
+public:
+
+  subselect_simplein_engine(THD *thd, st_join_table *tab_arg,
+			    Item_subselect *subs, Item *where)
+    :subselect_engine(thd, subs, 0), tab(tab_arg), cond(where)
+  {}
+    
+  int prepare();
+  void fix_length_and_dec(Item_cache** row);
+  int exec();
+  uint cols() { return 1; }
+  bool dependent() { return 1; }
+  bool uncacheable() { return 1; }
+  void  exclude();
+};

sql/sql_lex.h

@@ -283,7 +283,7 @@ class st_select_lex_unit: public st_select_lex_node {
   st_select_lex *return_to;
   /* LIMIT clause runtime counters */
   ha_rows select_limit_cnt, offset_limit_cnt;
-  /* not NULL if union used in subselect, point to subselect item */
+  /* not NULL if unit used in subselect, point to subselect item */
   Item_subselect *item;
   /* thread handler */
   THD *thd;

sql/sql_select.cc

@@ -32,7 +32,7 @@
 
 const char *join_type_str[]={ "UNKNOWN","system","const","eq_ref","ref",
 			      "MAYBE_REF","ALL","range","index","fulltext",
-			      "ref_or_null"
+			      "ref_or_null","simple_in"
 };
 
 static void optimize_keyuse(JOIN *join, DYNAMIC_ARRAY *keyuse_array);
@@ -723,6 +723,45 @@ JOIN::optimize()
 		     (select_lex->ftfunc_list->elements ? 
 		      SELECT_NO_JOIN_CACHE : 0));
 
+  /*
+    is this simple IN subquery?
+  */
+  if (!group_list && !order && !having &&
+      unit->item && unit->item->substype() == Item_subselect::IN_SUBS &&
+      tables == 1 && join_tab[0].type == JT_EQ_REF &&
+      conds &&
+      !unit->first_select()->next_select())
+  {
+    Item *where= 0;
+    bool ok= 0;
+    if (conds->type() == Item::FUNC_ITEM &&
+	((class Item_func *)this->conds)->functype() == Item_func::EQ_FUNC &&
+	((Item_func *)conds)->arguments()[0]->type() == Item::REF_ITEM &&
+	((Item_func *)conds)->arguments()[1]->type() == Item::FIELD_ITEM)
+    {
+      ok= 1;
+      join_tab->info= "Using index";
+    }
+    else if (conds->type() == Item::COND_ITEM &&
+	     ((class Item_func *)this->conds)->functype() ==
+	     Item_func::COND_AND_FUNC)
+    {
+      ok= 1;
+      where= conds;
+      join_tab->info= "Using index; Using where";
+    }
+
+    if (ok)
+    {
+      join_tab[0].type= JT_SIMPLE_IN;
+      error= 0;
+      DBUG_RETURN(unit->item->
+		  change_engine(new subselect_simplein_engine(thd, join_tab,
+							      unit->item,
+							      where)));
+    }
+  }
+
   /*
     Need to tell Innobase that to play it safe, it should fetch all
     columns of the tables: this is because MySQL may build row
@@ -5337,7 +5376,7 @@ flush_cached_records(JOIN *join,JOIN_TAB *join_tab,bool skipp_last)
 
 /* Help function when we get some an error from the table handler */
 
-static int report_error(TABLE *table, int error)
+int report_error(TABLE *table, int error)
 {
   if (error == HA_ERR_END_OF_FILE || error == HA_ERR_KEY_NOT_FOUND)
   {

sql/sql_select.h

@@ -75,7 +75,8 @@ typedef struct st_join_cache {
 */
 
 enum join_type { JT_UNKNOWN,JT_SYSTEM,JT_CONST,JT_EQ_REF,JT_REF,JT_MAYBE_REF,
-		 JT_ALL, JT_RANGE, JT_NEXT, JT_FT, JT_REF_OR_NULL};
+		 JT_ALL, JT_RANGE, JT_NEXT, JT_FT, JT_REF_OR_NULL,
+		 JT_SIMPLE_IN};
 
 class JOIN;
 
@@ -305,7 +306,6 @@ bool create_myisam_from_heap(THD *thd, TABLE *table, TMP_TABLE_PARAM *param,
 /* functions from opt_sum.cc */
 int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds);
 
-
 /* class to copying an field/item to a key struct */
 
 class store_key :public Sql_alloc
@@ -407,3 +407,4 @@ class store_key_const_item :public store_key_item
 bool cp_buffer_from_ref(TABLE_REF *ref);
 bool error_if_full_join(JOIN *join);
 void relink_tables(SELECT_LEX *select_lex);
+int report_error(TABLE *table, int error);