1 files changed, 98 insertions, 37 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 88ea01f9c68..92839eb0e5f 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -21,30 +21,24 @@
 #endif
 
 class st_select_lex;
+class st_select_lex_unit;
 class JOIN;
 class select_subselect;
+class subselect_engine;
 
 /* base class for subselects */
 
 class Item_subselect :public Item
 {
+  my_bool engine_owner; /* Is this item owner of engine */
+  my_bool value_assigned; /* value already assigned to subselect */
 protected:
+  /* engine that perform execution of subselect (single select or union) */
+  subselect_engine *engine; 
+  /* allowed number of columns (1 for single value subqueries) */
   uint max_columns;
-  my_bool assigned; /* value already assigned to subselect */
-  my_bool executed; /* simple subselect is executed */
-  my_bool optimized; /* simple subselect is optimized */
-  my_bool error; /* error in query */
 
-  int exec();
-  virtual void assign_null() 
-  {
-    null_value= 1;
-  }
 public:
-  st_select_lex *select_lex;
-  JOIN *join;
-  select_subselect *result;
-
   Item_subselect(THD *thd, st_select_lex *select_lex,
 		 select_subselect* result);
   Item_subselect(Item_subselect *item)
@@ -52,18 +46,22 @@ public:
     null_value= item->null_value;
     decimals= item->decimals;
     max_columns= item->max_columns;
-    assigned= item->assigned;
-    executed= item->executed;
-    select_lex= item->select_lex;
-    join= item->join;
-    result= item->result;
+    engine= item->engine;
+    engine_owner= 0;
     name= item->name;
-    error= item->error;
   }
+  ~Item_subselect();
+  virtual void assign_null() 
+  {
+    null_value= 1;
+  }
+  bool assigned() { return value_assigned; }
+  void assigned(bool a) { value_assigned= a; }
   enum Type type() const;
   bool is_null() { return null_value; }
   void make_field (Send_field *);
   bool fix_fields(THD *thd, TABLE_LIST *tables, Item **ref);
+  virtual void fix_length_and_dec();
   table_map used_tables() const;
 
   friend class select_subselect;
@@ -75,18 +73,10 @@ public:
 class Item_singleval_subselect :public Item_subselect
 {
 protected:
-  longlong int_value;
-  double real_value;
-  enum Item_result res_type;
+  longlong int_value; /* here stored integer value of this item */
+  double real_value; /* here stored real value of this item */
+  enum Item_result res_type; /* type of results */
 
-  virtual void assign_null() 
-  {
-    null_value= 1;
-    int_value= 0;
-    real_value= 0;
-    max_length= 4;
-    res_type= STRING_RESULT;
-  }
 public:
   Item_singleval_subselect(THD *thd, st_select_lex *select_lex);
   Item_singleval_subselect(Item_singleval_subselect *item):
@@ -98,12 +88,20 @@ public:
     decimals= item->decimals;
     res_type= item->res_type;
   }
+  virtual void assign_null() 
+  {
+    null_value= 1;
+    int_value= 0;
+    real_value= 0;
+    max_length= 4;
+    res_type= STRING_RESULT;
+  }
   double val ();
   longlong val_int ();
   String *val_str (String *);
   Item *new_item() { return new Item_singleval_subselect(this); }
   enum Item_result result_type() const { return res_type; }
-
+  void fix_length_and_dec();
   friend class select_singleval_subselect;
 };
 
@@ -112,12 +110,8 @@ public:
 class Item_exists_subselect :public Item_subselect
 {
 protected:
-  longlong value;
+  longlong value; /* value of this item (boolean: exists/not-exists) */
 
-  virtual void assign_null() 
-  {
-    value= 0;
-  }
 public:
   Item_exists_subselect(THD *thd, st_select_lex *select_lex);
   Item_exists_subselect(Item_exists_subselect *item):
@@ -125,11 +119,78 @@ public:
   {
     value= item->value;
   }
+  virtual void assign_null() 
+  {
+    value= 0;
+  }
+
   Item *new_item() { return new Item_exists_subselect(this); }
   enum Item_result result_type() const { return INT_RESULT;}
   longlong val_int();
   double val();
   String *val_str(String*);
-
+  void fix_length_and_dec();
   friend class select_exists_subselect;
 };
+
+class subselect_engine
+{
+protected:
+  select_subselect *result; /* results storage class */
+  THD *thd; /* pointer to current THD */
+  Item_subselect *item; /* item, that use this engine */
+  enum Item_result res_type; /* type of results */
+public:
+  static void *operator new(size_t size)
+  {
+    return (void*) sql_alloc((uint) size);
+  }
+  static void operator delete(void *ptr, size_t size) {}
+
+  subselect_engine(THD *thd, Item_subselect *si, select_subselect *res) 
+  {
+    result= res;
+    item= si;
+    this->thd= thd;
+    res_type= STRING_RESULT;
+  }
+
+  virtual int prepare()= 0;
+  virtual void fix_length_and_dec()= 0;
+  virtual int exec()= 0;
+  virtual uint cols()= 0; /* return number of columnss in select */
+  virtual bool depended()= 0; /* depended from outer select */
+  enum Item_result type() { return res_type; }
+};
+
+class subselect_single_select_engine: public subselect_engine
+{
+  my_bool executed; /* simple subselect is executed */
+  my_bool optimized; /* simple subselect is optimized */
+  st_select_lex *select_lex; /* corresponding select_lex */
+  JOIN * join; /* corresponding JOIN structure */
+public:
+  subselect_single_select_engine(THD *thd, st_select_lex *select,
+				 select_subselect *result,
+				 Item_subselect *item);
+  virtual int prepare();
+  virtual void fix_length_and_dec();
+  virtual int exec();
+  virtual uint cols();
+  virtual bool depended();
+};
+
+class subselect_union_engine: public subselect_engine
+{
+  st_select_lex_unit *unit;  /* corresponding unit structure */
+public:
+  subselect_union_engine(THD *thd,
+			 st_select_lex_unit *u,
+			 select_subselect *result,
+			 Item_subselect *item);
+  virtual int prepare();
+  virtual void fix_length_and_dec();
+  virtual int exec();
+  virtual uint cols();
+  virtual bool depended();
+};