Bug#43668: Wrong comparison and MIN/MAX for YEAR(2)

MySQL manual describes values of the YEAR(2) field type as follows:
values 00 - 69 mean 2000 - 2069 years and values 70 - 99 mean 1970 - 1999
years. MIN/MAX and comparison functions was comparing them as int values
thus producing wrong result.

Now the Arg_comparator class is extended with compare_year function which
performs correct comparison of the YEAR type.
The Item_sum_hybrid class now uses Item_cache and Arg_comparator objects to
correctly calculate its value.
To allow Arg_comparator to use func_name() function for Item_func and Item_sum
objects the func_name declaration is moved to the Item_result_field class.
A helper function is_owner_equal_func is added to the Arg_comparator class.
It checks whether the Arg_comparator object owner is the <=> function or not.
A helper function setup is added to the Item_sum_hybrid class. It sets up
cache item and comparator.

mysql-test/r/func_group.result

@@ -885,7 +885,7 @@ cast(sum(distinct df) as signed)
 3
 select cast(min(df) as signed) from t1;
 cast(min(df) as signed)
-0
+1
 select 1e8 * sum(distinct df) from t1;
 1e8 * sum(distinct df)
 330000000
@@ -1477,3 +1477,196 @@ COUNT(*)
 SET SQL_MODE=default;
 DROP TABLE t1;
 End of 5.0 tests
+#
+# Bug#43668: Wrong comparison and MIN/MAX for YEAR(2)
+#
+create table t1 (f1 year(2), f2 year(4), f3 date, f4 datetime);
+insert into t1 values
+(98,1998,19980101,"1998-01-01 00:00:00"),
+(00,2000,20000101,"2000-01-01 00:00:01"),
+(02,2002,20020101,"2002-01-01 23:59:59"),
+(60,2060,20600101,"2060-01-01 11:11:11"),
+(70,1970,19700101,"1970-11-11 22:22:22"),
+(NULL,NULL,NULL,NULL);
+select min(f1),max(f1) from t1;
+min(f1)	max(f1)
+70	60
+select min(f2),max(f2) from t1;
+min(f2)	max(f2)
+1970	2060
+select min(f3),max(f3) from t1;
+min(f3)	max(f3)
+1970-01-01	2060-01-01
+select min(f4),max(f4) from t1;
+min(f4)	max(f4)
+1970-11-11 22:22:22	2060-01-01 11:11:11
+select a.f1 as a, b.f1 as b, a.f1 > b.f1 as gt,
+a.f1 < b.f1 as lt, a.f1<=>b.f1 as eq
+from t1 a, t1 b;
+a	b	gt	lt	eq
+98	98	0	0	1
+00	98	1	0	0
+02	98	1	0	0
+60	98	1	0	0
+70	98	0	1	0
+NULL	98	NULL	NULL	0
+98	00	0	1	0
+00	00	0	0	1
+02	00	1	0	0
+60	00	1	0	0
+70	00	0	1	0
+NULL	00	NULL	NULL	0
+98	02	0	1	0
+00	02	0	1	0
+02	02	0	0	1
+60	02	1	0	0
+70	02	0	1	0
+NULL	02	NULL	NULL	0
+98	60	0	1	0
+00	60	0	1	0
+02	60	0	1	0
+60	60	0	0	1
+70	60	0	1	0
+NULL	60	NULL	NULL	0
+98	70	1	0	0
+00	70	1	0	0
+02	70	1	0	0
+60	70	1	0	0
+70	70	0	0	1
+NULL	70	NULL	NULL	0
+98	NULL	NULL	NULL	0
+00	NULL	NULL	NULL	0
+02	NULL	NULL	NULL	0
+60	NULL	NULL	NULL	0
+70	NULL	NULL	NULL	0
+NULL	NULL	NULL	NULL	1
+select a.f1 as a, b.f2 as b, a.f1 > b.f2 as gt,
+a.f1 < b.f2 as lt, a.f1<=>b.f2 as eq
+from t1 a, t1 b;
+a	b	gt	lt	eq
+98	1998	0	0	1
+00	1998	1	0	0
+02	1998	1	0	0
+60	1998	1	0	0
+70	1998	0	1	0
+NULL	1998	NULL	NULL	0
+98	2000	0	1	0
+00	2000	0	0	1
+02	2000	1	0	0
+60	2000	1	0	0
+70	2000	0	1	0
+NULL	2000	NULL	NULL	0
+98	2002	0	1	0
+00	2002	0	1	0
+02	2002	0	0	1
+60	2002	1	0	0
+70	2002	0	1	0
+NULL	2002	NULL	NULL	0
+98	2060	0	1	0
+00	2060	0	1	0
+02	2060	0	1	0
+60	2060	0	0	1
+70	2060	0	1	0
+NULL	2060	NULL	NULL	0
+98	1970	1	0	0
+00	1970	1	0	0
+02	1970	1	0	0
+60	1970	1	0	0
+70	1970	0	0	1
+NULL	1970	NULL	NULL	0
+98	NULL	NULL	NULL	0
+00	NULL	NULL	NULL	0
+02	NULL	NULL	NULL	0
+60	NULL	NULL	NULL	0
+70	NULL	NULL	NULL	0
+NULL	NULL	NULL	NULL	1
+select a.f1 as a, b.f3 as b, a.f1 > b.f3 as gt,
+a.f1 < b.f3 as lt, a.f1<=>b.f3 as eq
+from t1 a, t1 b;
+a	b	gt	lt	eq
+98	1998-01-01	0	1	0
+00	1998-01-01	1	0	0
+02	1998-01-01	1	0	0
+60	1998-01-01	1	0	0
+70	1998-01-01	0	1	0
+NULL	1998-01-01	NULL	NULL	0
+98	2000-01-01	0	1	0
+00	2000-01-01	0	1	0
+02	2000-01-01	1	0	0
+60	2000-01-01	1	0	0
+70	2000-01-01	0	1	0
+NULL	2000-01-01	NULL	NULL	0
+98	2002-01-01	0	1	0
+00	2002-01-01	0	1	0
+02	2002-01-01	0	1	0
+60	2002-01-01	1	0	0
+70	2002-01-01	0	1	0
+NULL	2002-01-01	NULL	NULL	0
+98	2060-01-01	0	1	0
+00	2060-01-01	0	1	0
+02	2060-01-01	0	1	0
+60	2060-01-01	0	1	0
+70	2060-01-01	0	1	0
+NULL	2060-01-01	NULL	NULL	0
+98	1970-01-01	1	0	0
+00	1970-01-01	1	0	0
+02	1970-01-01	1	0	0
+60	1970-01-01	1	0	0
+70	1970-01-01	0	1	0
+NULL	1970-01-01	NULL	NULL	0
+98	NULL	NULL	NULL	0
+00	NULL	NULL	NULL	0
+02	NULL	NULL	NULL	0
+60	NULL	NULL	NULL	0
+70	NULL	NULL	NULL	0
+NULL	NULL	NULL	NULL	1
+select a.f1 as a, b.f4 as b, a.f1 > b.f4 as gt,
+a.f1 < b.f4 as lt, a.f1<=>b.f4 as eq
+from t1 a, t1 b;
+a	b	gt	lt	eq
+98	1998-01-01 00:00:00	0	1	0
+00	1998-01-01 00:00:00	1	0	0
+02	1998-01-01 00:00:00	1	0	0
+60	1998-01-01 00:00:00	1	0	0
+70	1998-01-01 00:00:00	0	1	0
+NULL	1998-01-01 00:00:00	NULL	NULL	0
+98	2000-01-01 00:00:01	0	1	0
+00	2000-01-01 00:00:01	0	1	0
+02	2000-01-01 00:00:01	1	0	0
+60	2000-01-01 00:00:01	1	0	0
+70	2000-01-01 00:00:01	0	1	0
+NULL	2000-01-01 00:00:01	NULL	NULL	0
+98	2002-01-01 23:59:59	0	1	0
+00	2002-01-01 23:59:59	0	1	0
+02	2002-01-01 23:59:59	0	1	0
+60	2002-01-01 23:59:59	1	0	0
+70	2002-01-01 23:59:59	0	1	0
+NULL	2002-01-01 23:59:59	NULL	NULL	0
+98	2060-01-01 11:11:11	0	1	0
+00	2060-01-01 11:11:11	0	1	0
+02	2060-01-01 11:11:11	0	1	0
+60	2060-01-01 11:11:11	0	1	0
+70	2060-01-01 11:11:11	0	1	0
+NULL	2060-01-01 11:11:11	NULL	NULL	0
+98	1970-11-11 22:22:22	1	0	0
+00	1970-11-11 22:22:22	1	0	0
+02	1970-11-11 22:22:22	1	0	0
+60	1970-11-11 22:22:22	1	0	0
+70	1970-11-11 22:22:22	0	1	0
+NULL	1970-11-11 22:22:22	NULL	NULL	0
+98	NULL	NULL	NULL	0
+00	NULL	NULL	NULL	0
+02	NULL	NULL	NULL	0
+60	NULL	NULL	NULL	0
+70	NULL	NULL	NULL	0
+NULL	NULL	NULL	NULL	1
+select *, f1 = f2 from t1;
+f1	f2	f3	f4	f1 = f2
+98	1998	1998-01-01	1998-01-01 00:00:00	1
+00	2000	2000-01-01	2000-01-01 00:00:01	1
+02	2002	2002-01-01	2002-01-01 23:59:59	1
+60	2060	2060-01-01	2060-01-01 11:11:11	1
+70	1970	1970-01-01	1970-11-11 22:22:22	1
+NULL	NULL	NULL	NULL	NULL
+drop table t1;
+#

mysql-test/t/func_group.test

@@ -1006,3 +1006,35 @@ DROP TABLE t1;
 
 ###
 --echo End of 5.0 tests
+
+--echo #
+--echo # Bug#43668: Wrong comparison and MIN/MAX for YEAR(2)
+--echo #
+create table t1 (f1 year(2), f2 year(4), f3 date, f4 datetime);
+insert into t1 values
+  (98,1998,19980101,"1998-01-01 00:00:00"),
+  (00,2000,20000101,"2000-01-01 00:00:01"),
+  (02,2002,20020101,"2002-01-01 23:59:59"),
+  (60,2060,20600101,"2060-01-01 11:11:11"),
+  (70,1970,19700101,"1970-11-11 22:22:22"),
+  (NULL,NULL,NULL,NULL);
+select min(f1),max(f1) from t1;
+select min(f2),max(f2) from t1;
+select min(f3),max(f3) from t1;
+select min(f4),max(f4) from t1;
+select a.f1 as a, b.f1 as b, a.f1 > b.f1 as gt,
+       a.f1 < b.f1 as lt, a.f1<=>b.f1 as eq
+from t1 a, t1 b;
+select a.f1 as a, b.f2 as b, a.f1 > b.f2 as gt,
+       a.f1 < b.f2 as lt, a.f1<=>b.f2 as eq
+from t1 a, t1 b;
+select a.f1 as a, b.f3 as b, a.f1 > b.f3 as gt,
+       a.f1 < b.f3 as lt, a.f1<=>b.f3 as eq
+from t1 a, t1 b;
+select a.f1 as a, b.f4 as b, a.f1 > b.f4 as gt,
+       a.f1 < b.f4 as lt, a.f1<=>b.f4 as eq
+from t1 a, t1 b;
+select *, f1 = f2 from t1;
+drop table t1;
+--echo #
+

sql/item.cc

@@ -6940,7 +6940,7 @@ Item_cache* Item_cache::get_cache(const Item *item)
 {
   switch (item->result_type()) {
   case INT_RESULT:
-    return new Item_cache_int();
+    return new Item_cache_int(item->field_type());
   case REAL_RESULT:
     return new Item_cache_real();
   case DECIMAL_RESULT:

sql/item.h

@@ -2135,6 +2135,23 @@ class Item_result_field :public Item	/* Item with result field */
     save_in_field(result_field, no_conversions);
   }
   void cleanup();
+  /*
+    This method is used for debug purposes to print the name of an
+    item to the debug log. The second use of this method is as
+    a helper function of print() and error messages, where it is
+    applicable. To suit both goals it should return a meaningful,
+    distinguishable and sintactically correct string. This method
+    should not be used for runtime type identification, use enum
+    {Sum}Functype and Item_func::functype()/Item_sum::sum_func()
+    instead.
+    Added here, to the parent class of both Item_func and Item_sum_func.
+
+    NOTE: for Items inherited from Item_sum, func_name() return part of
+    function name till first argument (including '(') to make difference in
+    names for functions with 'distinct' clause and without 'distinct' and
+    also to make printing of items inherited from Item_sum uniform.
+  */
+  virtual const char *func_name() const= 0;
 };
 
 

sql/item_cmpfunc.h

@@ -32,7 +32,7 @@ class Arg_comparator: public Sql_alloc
 {
   Item **a, **b;
   arg_cmp_func func;
-  Item_bool_func2 *owner;
+  Item_result_field *owner;
   Arg_comparator *comparators;   // used only for compare_row()
   double precision;
   /* Fields used in DATE/DATETIME comparison. */
@@ -40,30 +40,42 @@ class Arg_comparator: public Sql_alloc
   enum_field_types a_type, b_type; // Types of a and b items
   Item *a_cache, *b_cache;         // Cached values of a and b items
   bool is_nulls_eq;                // TRUE <=> compare for the EQUAL_FUNC
+  bool set_null;                   // TRUE <=> set owner->null_value
+                                   //   when one of arguments is NULL.
+  bool year_as_datetime;           // TRUE <=> convert YEAR value to
+                                   // the YYYY-00-00 00:00:00 DATETIME
+                                   // format. See compare_year.
   enum enum_date_cmp_type { CMP_DATE_DFLT= 0, CMP_DATE_WITH_DATE,
                             CMP_DATE_WITH_STR, CMP_STR_WITH_DATE };
-  longlong (*get_value_func)(THD *thd, Item ***item_arg, Item **cache_arg,
-                             Item *warn_item, bool *is_null);
+  longlong (*get_value_a_func)(THD *thd, Item ***item_arg, Item **cache_arg,
+                               Item *warn_item, bool *is_null);
+  longlong (*get_value_b_func)(THD *thd, Item ***item_arg, Item **cache_arg,
+                               Item *warn_item, bool *is_null);
 public:
   DTCollation cmp_collation;
+  /* Allow owner function to use string buffers. */
+  String value1, value2;
 
-  Arg_comparator(): thd(0), a_cache(0), b_cache(0) {};
+  Arg_comparator(): thd(0), a_cache(0), b_cache(0), set_null(0),
+    year_as_datetime(0), get_value_a_func(0), get_value_b_func(0) {};
   Arg_comparator(Item **a1, Item **a2): a(a1), b(a2), thd(0),
-    a_cache(0), b_cache(0) {};
+    a_cache(0), b_cache(0), set_null(0), year_as_datetime(0),
+    get_value_a_func(0), get_value_b_func(0) {};
 
-  int set_compare_func(Item_bool_func2 *owner, Item_result type);
-  inline int set_compare_func(Item_bool_func2 *owner_arg)
+  int set_compare_func(Item_result_field *owner, Item_result type);
+  inline int set_compare_func(Item_result_field *owner_arg)
   {
     return set_compare_func(owner_arg, item_cmp_type((*a)->result_type(),
                                                      (*b)->result_type()));
   }
-  int set_cmp_func(Item_bool_func2 *owner_arg,
+  int set_cmp_func(Item_result_field *owner_arg,
 			  Item **a1, Item **a2,
 			  Item_result type);
 
-  inline int set_cmp_func(Item_bool_func2 *owner_arg,
-			  Item **a1, Item **a2)
+  inline int set_cmp_func(Item_result_field *owner_arg,
+			  Item **a1, Item **a2, bool set_null_arg)
   {
+    set_null= set_null_arg;
     return set_cmp_func(owner_arg, a1, a2,
                         item_cmp_type((*a1)->result_type(),
                                       (*a2)->result_type()));
@@ -89,12 +101,18 @@ class Arg_comparator: public Sql_alloc
   int compare_real_fixed();
   int compare_e_real_fixed();
   int compare_datetime();        // compare args[0] & args[1] as DATETIMEs
+  int compare_year();
 
   static enum enum_date_cmp_type can_compare_as_dates(Item *a, Item *b,
                                                       ulonglong *const_val_arg);
 
-  void set_datetime_cmp_func(Item **a1, Item **b1);
+  void set_datetime_cmp_func(Item_result_field *owner_arg, Item **a1, Item **b1);
   static arg_cmp_func comparator_matrix [5][2];
+  inline bool is_owner_equal_func()
+  {
+    return (owner->type() == Item::FUNC_ITEM &&
+           ((Item_func*)owner)->functype() == Item_func::EQUAL_FUNC);
+  }
 
   friend class Item_func;
 };
@@ -324,7 +342,6 @@ class Item_bool_func2 :public Item_int_func
 {						/* Bool with 2 string args */
 protected:
   Arg_comparator cmp;
-  String tmp_value1,tmp_value2;
   bool abort_on_null;
 
 public:
@@ -333,7 +350,7 @@ class Item_bool_func2 :public Item_int_func
   void fix_length_and_dec();
   void set_cmp_func()
   {
-    cmp.set_cmp_func(this, tmp_arg, tmp_arg+1);
+    cmp.set_cmp_func(this, tmp_arg, tmp_arg+1, TRUE);
   }
   optimize_type select_optimize() const { return OPTIMIZE_OP; }
   virtual enum Functype rev_functype() const { return UNKNOWN_FUNC; }

sql/item_func.h

@@ -124,17 +124,6 @@ class Item_func :public Item_result_field
   virtual optimize_type select_optimize() const { return OPTIMIZE_NONE; }
   virtual bool have_rev_func() const { return 0; }
   virtual Item *key_item() const { return args[0]; }
-  /*
-    This method is used for debug purposes to print the name of an
-    item to the debug log. The second use of this method is as
-    a helper function of print(), where it is applicable.
-    To suit both goals it should return a meaningful,
-    distinguishable and sintactically correct string.  This method
-    should not be used for runtime type identification, use enum
-    {Sum}Functype and Item_func::functype()/Item_sum::sum_func()
-    instead.
-  */
-  virtual const char *func_name() const= 0;
   virtual bool const_item() const { return const_item_cache; }
   inline Item **arguments() const { return args; }
   void set_arguments(List<Item> &list);

sql/item_geofunc.cc

@@ -506,8 +506,8 @@ String *Item_func_spatial_collection::val_str(String *str)
 longlong Item_func_spatial_rel::val_int()
 {
   DBUG_ASSERT(fixed == 1);
-  String *res1= args[0]->val_str(&tmp_value1);
-  String *res2= args[1]->val_str(&tmp_value2);
+  String *res1= args[0]->val_str(&cmp.value1);
+  String *res2= args[1]->val_str(&cmp.value2);
   Geometry_buffer buffer1, buffer2;
   Geometry *g1, *g2;
   MBR mbr1, mbr2;

sql/item_subselect.h

@@ -132,6 +132,7 @@ class Item_subselect :public Item_result_field
     @return the SELECT_LEX structure associated with this Item
   */
   st_select_lex* get_select_lex();
+  const char *func_name() const { DBUG_ASSERT(0); return "subselect"; }
 
   friend class select_subselect;
   friend class Item_in_optimizer;

sql/item_sum.cc

@@ -614,35 +614,6 @@ Item_sum_num::fix_fields(THD *thd, Item **ref)
 }
 
 
-Item_sum_hybrid::Item_sum_hybrid(THD *thd, Item_sum_hybrid *item)
-  :Item_sum(thd, item), value(item->value), hybrid_type(item->hybrid_type),
-  hybrid_field_type(item->hybrid_field_type), cmp_sign(item->cmp_sign),
-  was_values(item->was_values)
-{
-  /* copy results from old value */
-  switch (hybrid_type) {
-  case INT_RESULT:
-    sum_int= item->sum_int;
-    break;
-  case DECIMAL_RESULT:
-    my_decimal2decimal(&item->sum_dec, &sum_dec);
-    break;
-  case REAL_RESULT:
-    sum= item->sum;
-    break;
-  case STRING_RESULT:
-    /*
-      This can happen with ROLLUP. Note that the value is already
-      copied at function call.
-    */
-    break;
-  case ROW_RESULT:
-  default:
-    DBUG_ASSERT(0);
-  }
-  collation.set(item->collation);
-}
-
 bool
 Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
 {
@@ -662,15 +633,12 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
   switch (hybrid_type= item->result_type()) {
   case INT_RESULT:
     max_length= 20;
-    sum_int= 0;
     break;
   case DECIMAL_RESULT:
     max_length= item->max_length;
-    my_decimal_set_zero(&sum_dec);
     break;
   case REAL_RESULT:
     max_length= float_length(decimals);
-    sum= 0.0;
     break;
   case STRING_RESULT:
     max_length= item->max_length;
@@ -679,10 +647,10 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
   default:
     DBUG_ASSERT(0);
   };
+  setup(args[0], NULL);
   /* MIN/MAX can return NULL for empty set indepedent of the used column */
   maybe_null= 1;
   unsigned_flag=item->unsigned_flag;
-  collation.set(item->collation);
   result_field=0;
   null_value=1;
   fix_length_and_dec();
@@ -700,6 +668,31 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
   return FALSE;
 }
 
+
+/**
+  MIN/MAX function setup.
+
+  @param item       argument of MIN/MAX function
+  @param value_arg  calculated value of MIN/MAX function
+
+  @details
+    Setup cache/comparator of MIN/MAX functions. When called by the
+    copy_or_same function value_arg parameter contains calculated value
+    of the original MIN/MAX object and it is saved in this object's cache.
+*/
+
+void Item_sum_hybrid::setup(Item *item, Item *value_arg)
+{
+  value= Item_cache::get_cache(item);
+  value->setup(item);
+  if (value_arg)
+    value->store(value_arg);
+  cmp= new Arg_comparator();
+  cmp->set_cmp_func(this, args, (Item**)&value, FALSE);
+  collation.set(item->collation);
+}
+
+
 Field *Item_sum_hybrid::create_tmp_field(bool group, TABLE *table,
 					 uint convert_blob_length)
 {
@@ -1591,19 +1584,7 @@ void Item_sum_variance::update_field()
 
 void Item_sum_hybrid::clear()
 {
-  switch (hybrid_type) {
-  case INT_RESULT:
-    sum_int= 0;
-    break;
-  case DECIMAL_RESULT:
-    my_decimal_set_zero(&sum_dec);
-    break;
-  case REAL_RESULT:
-    sum= 0.0;
-    break;
-  default:
-    value.length(0);
-  }
+  value->null_value= 1;
   null_value= 1;
 }
 
@@ -1612,30 +1593,7 @@ double Item_sum_hybrid::val_real()
   DBUG_ASSERT(fixed == 1);
   if (null_value)
     return 0.0;
-  switch (hybrid_type) {
-  case STRING_RESULT:
-  {
-    char *end_not_used;
-    int err_not_used;
-    String *res;  res=val_str(&str_value);
-    return (res ? my_strntod(res->charset(), (char*) res->ptr(), res->length(),
-			     &end_not_used, &err_not_used) : 0.0);
-  }
-  case INT_RESULT:
-    if (unsigned_flag)
-      return ulonglong2double(sum_int);
-    return (double) sum_int;
-  case DECIMAL_RESULT:
-    my_decimal2double(E_DEC_FATAL_ERROR, &sum_dec, &sum);
-    return sum;
-  case REAL_RESULT:
-    return sum;
-  case ROW_RESULT:
-  default:
-    // This case should never be choosen
-    DBUG_ASSERT(0);
-    return 0;
-  }
+  return value->val_real();
 }
 
 longlong Item_sum_hybrid::val_int()
@@ -1643,18 +1601,7 @@ longlong Item_sum_hybrid::val_int()
   DBUG_ASSERT(fixed == 1);
   if (null_value)
     return 0;
-  switch (hybrid_type) {
-  case INT_RESULT:
-    return sum_int;
-  case DECIMAL_RESULT:
-  {
-    longlong result;
-    my_decimal2int(E_DEC_FATAL_ERROR, &sum_dec, unsigned_flag, &result);
-    return sum_int;
-  }
-  default:
-    return (longlong) rint(Item_sum_hybrid::val_real());
-  }
+  return value->val_int();
 }
 
 
@@ -1663,26 +1610,7 @@ my_decimal *Item_sum_hybrid::val_decimal(my_decimal *val)
   DBUG_ASSERT(fixed == 1);
   if (null_value)
     return 0;
-  switch (hybrid_type) {
-  case STRING_RESULT:
-    string2my_decimal(E_DEC_FATAL_ERROR, &value, val);
-    break;
-  case REAL_RESULT:
-    double2my_decimal(E_DEC_FATAL_ERROR, sum, val);
-    break;
-  case DECIMAL_RESULT:
-    val= &sum_dec;
-    break;
-  case INT_RESULT:
-    int2my_decimal(E_DEC_FATAL_ERROR, sum_int, unsigned_flag, val);
-    break;
-  case ROW_RESULT:
-  default:
-    // This case should never be choosen
-    DBUG_ASSERT(0);
-    break;
-  }
-  return val;					// Keep compiler happy
+  return value->val_decimal(val);
 }
 
 
@@ -1692,25 +1620,7 @@ Item_sum_hybrid::val_str(String *str)
   DBUG_ASSERT(fixed == 1);
   if (null_value)
     return 0;
-  switch (hybrid_type) {
-  case STRING_RESULT:
-    return &value;
-  case REAL_RESULT:
-    str->set_real(sum,decimals, &my_charset_bin);
-    break;
-  case DECIMAL_RESULT:
-    my_decimal2string(E_DEC_FATAL_ERROR, &sum_dec, 0, 0, 0, str);
-    return str;
-  case INT_RESULT:
-    str->set_int(sum_int, unsigned_flag, &my_charset_bin);
-    break;
-  case ROW_RESULT:
-  default:
-    // This case should never be choosen
-    DBUG_ASSERT(0);
-    break;
-  }
-  return str;					// Keep compiler happy
+  return value->val_str(str);
 }
 
 
@@ -1719,7 +1629,9 @@ void Item_sum_hybrid::cleanup()
   DBUG_ENTER("Item_sum_hybrid::cleanup");
   Item_sum::cleanup();
   forced_const= FALSE;
-
+  if (cmp)
+    delete cmp;
+  cmp= 0;
   /*
     by default it is TRUE to avoid TRUE reporting by
     Item_func_not_all/Item_func_nop_all if this item was never called.
@@ -1740,63 +1652,21 @@ void Item_sum_hybrid::no_rows_in_result()
 
 Item *Item_sum_min::copy_or_same(THD* thd)
 {
-  return new (thd->mem_root) Item_sum_min(thd, this);
+  Item_sum_min *item= new (thd->mem_root) Item_sum_min(thd, this);
+  item->setup(args[0], value);
+  return item;
 }
 
 
 bool Item_sum_min::add()
 {
-  switch (hybrid_type) {
-  case STRING_RESULT:
+  /* args[0] < value */
+  int res= cmp->compare();
+  if (!args[0]->null_value &&
+      (null_value || res < 0))
   {
-    String *result=args[0]->val_str(&tmp_value);
-    if (!args[0]->null_value &&
-	(null_value || sortcmp(&value,result,collation.collation) > 0))
-    {
-      value.copy(*result);
-      null_value=0;
-    }
-  }
-  break;
-  case INT_RESULT:
-  {
-    longlong nr=args[0]->val_int();
-    if (!args[0]->null_value && (null_value ||
-				 (unsigned_flag && 
-				  (ulonglong) nr < (ulonglong) sum_int) ||
-				 (!unsigned_flag && nr < sum_int)))
-    {
-      sum_int=nr;
-      null_value=0;
-    }
-  }
-  break;
-  case DECIMAL_RESULT:
-  {
-    my_decimal value_buff, *val= args[0]->val_decimal(&value_buff);
-    if (!args[0]->null_value &&
-        (null_value || (my_decimal_cmp(&sum_dec, val) > 0)))
-    {
-      my_decimal2decimal(val, &sum_dec);
-      null_value= 0;
-    }
-  }
-  break;
-  case REAL_RESULT:
-  {
-    double nr= args[0]->val_real();
-    if (!args[0]->null_value && (null_value || nr < sum))
-    {
-      sum=nr;
-      null_value=0;
-    }
-  }
-  break;
-  case ROW_RESULT:
-  default:
-    // This case should never be choosen
-    DBUG_ASSERT(0);
-    break;
+    value->store(args[0]);
+    null_value= 0;
   }
   return 0;
 }
@@ -1804,63 +1674,21 @@ bool Item_sum_min::add()
 
 Item *Item_sum_max::copy_or_same(THD* thd)
 {
-  return new (thd->mem_root) Item_sum_max(thd, this);
+  Item_sum_max *item= new (thd->mem_root) Item_sum_max(thd, this);
+  item->setup(args[0], value);
+  return item;
 }
 
 
 bool Item_sum_max::add()
 {
-  switch (hybrid_type) {
-  case STRING_RESULT:
+  /* args[0] > value */
+  int res= cmp->compare();
+  if (!args[0]->null_value &&
+      (null_value || res > 0))
   {
-    String *result=args[0]->val_str(&tmp_value);
-    if (!args[0]->null_value &&
-	(null_value || sortcmp(&value,result,collation.collation) < 0))
-    {
-      value.copy(*result);
-      null_value=0;
-    }
-  }
-  break;
-  case INT_RESULT:
-  {
-    longlong nr=args[0]->val_int();
-    if (!args[0]->null_value && (null_value ||
-				 (unsigned_flag && 
-				  (ulonglong) nr > (ulonglong) sum_int) ||
-				 (!unsigned_flag && nr > sum_int)))
-    {
-      sum_int=nr;
-      null_value=0;
-    }
-  }
-  break;
-  case DECIMAL_RESULT:
-  {
-    my_decimal value_buff, *val= args[0]->val_decimal(&value_buff);
-    if (!args[0]->null_value &&
-        (null_value || (my_decimal_cmp(val, &sum_dec) > 0)))
-    {
-      my_decimal2decimal(val, &sum_dec);
-      null_value= 0;
-    }
-  }
-  break;
-  case REAL_RESULT:
-  {
-    double nr= args[0]->val_real();
-    if (!args[0]->null_value && (null_value || nr > sum))
-    {
-      sum=nr;
-      null_value=0;
-    }
-  }
-  break;
-  case ROW_RESULT:
-  default:
-    // This case should never be choosen
-    DBUG_ASSERT(0);
-    break;
+    value->store(args[0]);
+    null_value= 0;
   }
   return 0;
 }
@@ -2225,14 +2053,15 @@ void Item_sum_hybrid::update_field()
 void
 Item_sum_hybrid::min_max_update_str_field()
 {
-  String *res_str=args[0]->val_str(&value);
+  DBUG_ASSERT(cmp);
+  String *res_str=args[0]->val_str(&cmp->value1);
 
   if (!args[0]->null_value)
   {
-    result_field->val_str(&tmp_value);
+    result_field->val_str(&cmp->value2);
 
     if (result_field->is_null() ||
-	(cmp_sign * sortcmp(res_str,&tmp_value,collation.collation)) < 0)
+	(cmp_sign * sortcmp(res_str,&cmp->value2,collation.collation)) < 0)
       result_field->store(res_str->ptr(),res_str->length(),res_str->charset());
     result_field->set_notnull();
   }

sql/item_sum.h

@@ -323,22 +323,6 @@ class Item_sum :public Item_result_field
   virtual void update_field()=0;
   virtual bool keep_field_type(void) const { return 0; }
   virtual void fix_length_and_dec() { maybe_null=1; null_value=1; }
-  /*
-    This method is used for debug purposes to print the name of an
-    item to the debug log. The second use of this method is as
-    a helper function of print(), where it is applicable.
-    To suit both goals it should return a meaningful,
-    distinguishable and sintactically correct string.  This method
-    should not be used for runtime type identification, use enum
-    {Sum}Functype and Item_func::functype()/Item_sum::sum_func()
-    instead.
-
-    NOTE: for Items inherited from Item_sum, func_name() return part of
-    function name till first argument (including '(') to make difference in
-    names for functions with 'distinct' clause and without 'distinct' and
-    also to make printing of items inherited from Item_sum uniform.
-  */
-  virtual const char *func_name() const= 0;
   virtual Item *result_item(Field *field)
     { return new Item_field(field); }
   table_map used_tables() const { return used_tables_cache; }
@@ -664,6 +648,7 @@ class Item_avg_field :public Item_result_field
   }
   void fix_length_and_dec() {}
   enum Item_result result_type () const { return hybrid_type; }
+  const char *func_name() const { DBUG_ASSERT(0); return "avg_field"; }
 };
 
 
@@ -732,6 +717,7 @@ class Item_variance_field :public Item_result_field
   }
   void fix_length_and_dec() {}
   enum Item_result result_type () const { return hybrid_type; }
+  const char *func_name() const { DBUG_ASSERT(0); return "variance_field"; }
 };
 
 
@@ -807,6 +793,7 @@ class Item_std_field :public Item_variance_field
   my_decimal *val_decimal(my_decimal *);
   enum Item_result result_type () const { return REAL_RESULT; }
   enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE;}
+  const char *func_name() const { DBUG_ASSERT(0); return "std_field"; }
 };
 
 /*
@@ -832,14 +819,13 @@ class Item_sum_std :public Item_sum_variance
 };
 
 // This class is a string or number function depending on num_func
-
+class Arg_comparator;
+class Item_cache;
 class Item_sum_hybrid :public Item_sum
 {
 protected:
-  String value,tmp_value;
-  double sum;
-  longlong sum_int;
-  my_decimal sum_dec;
+  Item_cache *value;
+  Arg_comparator *cmp;
   Item_result hybrid_type;
   enum_field_types hybrid_field_type;
   int cmp_sign;
@@ -847,12 +833,17 @@ class Item_sum_hybrid :public Item_sum
 
   public:
   Item_sum_hybrid(Item *item_par,int sign)
-    :Item_sum(item_par), sum(0.0), sum_int(0),
+    :Item_sum(item_par), value(0), cmp(0),
     hybrid_type(INT_RESULT), hybrid_field_type(MYSQL_TYPE_LONGLONG),
     cmp_sign(sign), was_values(TRUE)
   { collation.set(&my_charset_bin); }
-  Item_sum_hybrid(THD *thd, Item_sum_hybrid *item);
+  Item_sum_hybrid(THD *thd, Item_sum_hybrid *item)
+    :Item_sum(thd, item), value(item->value), hybrid_type(item->hybrid_type),
+    hybrid_field_type(item->hybrid_field_type), cmp_sign(item->cmp_sign),
+    was_values(item->was_values)
+  { }
   bool fix_fields(THD *, Item **);
+  void setup(Item *item, Item *value_arg);
   void clear();
   double val_real();
   longlong val_int();