WL#926 "SUM(DISTINCT) and AVG(DISTINCT)": improvement of SUM(DISTINCT) and

 implementation of AVG(DISTINCT) which utilizes the approach with Fields.
The patch implemented in October is portede to the up-to-date tree 
containing DECIMAL type.
Tests for AVG(DISTINCT) (although there is not much to test provided
that SUM(DISTINCT) works), cleanups for COUNT(DISTINCT) and GROUP_CONCAT()
will follow in another changeset.


sql/field.cc:
  A handy way to init create_field used for use with virtual tmp tables.
  Feel free to extend it for your own needs.
sql/field.h:
  Declaration for create_field::init_for_tmp_table()
sql/item.cc:
  Implementation for a framework used to easily handle different result
  types of SQL expressions. Instead of having instances of each possible 
  result type (integer, decimal, double) in every item, variables
  of all used types are moved to struct Hybrid_type.
  Hybrid_type can change its dynamic type in runtime, and become,
  for instance, DECIMAL from INTEGER.
  All type-specific Item operations are moved to the class hierarchy
  Hybrid_type_traits. Item::decimals and Item::max_length can
  be moved to Hybrid_type as well.
sql/item.h:
  Declaration for Hybrid_type framework. See also comments for item.cc
  in this changeset.
sql/item_sum.cc:
  Rewritten implementation for Item_sum_sum_distinct (SUM(DISTINCT))
  and added implementation for Item_sum_avg_distinct (AVG(DISTINCT)).
  The classes utilize Hybrid_type class hierarchy and Fields to
  convert SUM/AVG arguments to binary representation and store in a RB-tree.
sql/item_sum.h:
  Declarations for Item_sum_distinct (the new intermediate class used
  for SUM and AVG distinct), Item_sum_sum_distinct, Item_sum_avg_distinct.
sql/sql_select.cc:
  Implementatio of create_virtual_tmp_table().
sql/sql_select.h:
  Declaration for create_virtual_tmp_table.
sql/sql_yacc.yy:
  Grammar support for Item_sum_avg_distinct.

sql/field.cc

@@ -7150,6 +7150,24 @@ void create_field::create_length_to_internal_length(void)
 }
 
 
+void create_field::init_for_tmp_table(enum_field_types sql_type_arg,
+                                      uint32 length_arg, uint32 decimals,
+                                      bool maybe_null, bool is_unsigned)
+{
+  field_name= "";
+  sql_type= sql_type_arg;
+  length= length_arg;;
+  unireg_check= Field::NONE;
+  interval= 0;
+  charset= &my_charset_bin;
+  geom_type= Field::GEOM_GEOMETRY;
+  pack_flag= (FIELDFLAG_NUMBER |
+              ((decimals & FIELDFLAG_MAX_DEC) << FIELDFLAG_DEC_SHIFT) |
+              (maybe_null ? FIELDFLAG_MAYBE_NULL : 0) |
+              (is_unsigned ? 0 : FIELDFLAG_DECIMAL));
+}
+
+
 enum_field_types get_blob_type_from_length(ulong length)
 {
   enum_field_types type;

sql/field.h

@@ -1340,7 +1340,8 @@ public:
   Create field class for CREATE TABLE
 */
 
-class create_field :public Sql_alloc {
+class create_field :public Sql_alloc
+{
 public:
   const char *field_name;
   const char *change;			// If done with alter table
@@ -1362,6 +1363,11 @@ public:
   create_field() :after(0) {}
   create_field(Field *field, Field *orig_field);
   void create_length_to_internal_length(void);
+
+  /* Init for a tmp table field. To be extended if need be. */
+  void init_for_tmp_table(enum_field_types sql_type_arg,
+                          uint32 max_length, uint32 decimals,
+                          bool maybe_null, bool is_unsigned);
 };
 
 

sql/item.cc

@@ -33,6 +33,131 @@ static void mark_as_dependent(THD *thd,
 
 const String my_null_string("NULL", 4, default_charset_info);
 
+/****************************************************************************/
+
+/* Hybrid_type_traits {_real} */
+
+void Hybrid_type_traits::fix_length_and_dec(Item *item, Item *arg) const
+{
+  item->decimals= NOT_FIXED_DEC;
+  item->max_length= item->float_length(arg->decimals);
+}
+
+
+const Hybrid_type_traits *Hybrid_type_traits::instance()
+{
+  const static Hybrid_type_traits real_traits;
+  return &real_traits;
+}
+
+
+my_decimal *
+Hybrid_type_traits::val_decimal(Hybrid_type *val, my_decimal *to) const
+{
+  double2my_decimal(E_DEC_FATAL_ERROR, val->real, val->dec_buf);
+  return val->dec_buf;
+}
+
+
+String *
+Hybrid_type_traits::val_str(Hybrid_type *val, String *to, uint8 decimals) const
+{
+  to->set(val->real, decimals, &my_charset_bin);
+  return to;
+}
+
+/* Hybrid_type_traits_decimal */
+
+const Hybrid_type_traits_decimal *Hybrid_type_traits_decimal::instance()
+{
+  const static Hybrid_type_traits_decimal decimal_traits;
+  return &decimal_traits;
+}
+
+
+void
+Hybrid_type_traits_decimal::fix_length_and_dec(Item *item, Item *arg) const
+{
+  item->decimals= arg->decimals;
+  item->max_length= min(arg->max_length + DECIMAL_LONGLONG_DIGITS,
+                        DECIMAL_MAX_LENGTH);
+}
+
+
+void Hybrid_type_traits_decimal::set_zero(Hybrid_type *val) const
+{
+  my_decimal_set_zero(&val->dec_buf[0]);
+  val->used_dec_buf_no= 0;
+}
+
+
+void Hybrid_type_traits_decimal::add(Hybrid_type *val, Field *f) const
+{
+  my_decimal_add(E_DEC_FATAL_ERROR,
+                 &val->dec_buf[val->used_dec_buf_no ^ 1],
+                 &val->dec_buf[val->used_dec_buf_no],
+                 f->val_decimal(&val->dec_buf[2]));
+  val->used_dec_buf_no^= 1;
+}
+
+
+void Hybrid_type_traits_decimal::div(Hybrid_type *val, ulonglong u) const
+{
+  int2my_decimal(E_DEC_FATAL_ERROR, u, TRUE, &val->dec_buf[2]);
+  /* XXX: what is '4' for scale? */
+  my_decimal_div(E_DEC_FATAL_ERROR,
+                 &val->dec_buf[val->used_dec_buf_no ^ 1],
+                 &val->dec_buf[val->used_dec_buf_no],
+                 &val->dec_buf[2], 4);
+  val->used_dec_buf_no^= 1;
+}
+
+
+longlong
+Hybrid_type_traits_decimal::val_int(Hybrid_type *val, bool unsigned_flag) const
+{
+  longlong result;
+  my_decimal2int(E_DEC_FATAL_ERROR, &val->dec_buf[val->used_dec_buf_no],
+                 unsigned_flag, &result);
+  return result;
+}
+
+
+double
+Hybrid_type_traits_decimal::val_real(Hybrid_type *val) const
+{
+  my_decimal2double(E_DEC_FATAL_ERROR, &val->dec_buf[val->used_dec_buf_no],
+                    &val->real);
+  return val->real;
+}
+
+
+String *
+Hybrid_type_traits_decimal::val_str(Hybrid_type *val, String *to,
+                                    uint8 decimals) const
+{
+  my_decimal_round(E_DEC_FATAL_ERROR, &val->dec_buf[val->used_dec_buf_no],
+                   decimals, FALSE, &val->dec_buf[2]);
+  my_decimal2string(E_DEC_FATAL_ERROR, &val->dec_buf[2], 0, 0, 0, to);
+  return to;
+}
+
+/* Hybrid_type_traits_integer */
+
+const Hybrid_type_traits_integer *Hybrid_type_traits_integer::instance()
+{
+  const static Hybrid_type_traits_integer integer_traits;
+  return &integer_traits;
+}
+
+void
+Hybrid_type_traits_integer::fix_length_and_dec(Item *item, Item *arg) const
+{
+  item->decimals= 0;
+  item->max_length= 21;
+  item->unsigned_flag= 0;
+}
+
 /*****************************************************************************
 ** Item functions
 *****************************************************************************/

sql/item.h

@@ -106,6 +106,120 @@ public:
   }
 };
 
+
+/*************************************************************************/
+/*
+  A framework to easily handle different return types for hybrid items
+  (hybrid item is an item whose operand can be of any type, e.g. integer,
+  real, decimal).
+*/
+
+struct Hybrid_type_traits;
+
+struct Hybrid_type
+{
+  longlong integer;
+
+  double real;
+  /*
+    Use two decimal buffers interchangeably to speed up += operation
+    which has no native support in decimal library.
+    Hybrid_type+= arg is implemented as dec_buf[1]= dec_buf[0] + arg.
+    The third decimal is used as a handy temporary storage.
+  */
+  my_decimal dec_buf[3];
+  int used_dec_buf_no;
+
+  /*
+    Traits moved to a separate class to
+      a) be able to easily change object traits in runtime
+      b) they work as a differentiator for the union above
+  */
+  const Hybrid_type_traits *traits;
+
+  Hybrid_type() {}
+  /* XXX: add traits->copy() when needed */
+  Hybrid_type(const Hybrid_type &rhs) :traits(rhs.traits) {}
+};
+
+
+/* Hybryd_type_traits interface + default implementation for REAL_RESULT */
+
+struct Hybrid_type_traits
+{
+  virtual Item_result type() const { return REAL_RESULT; }
+
+  virtual void
+  fix_length_and_dec(Item *item, Item *arg) const;
+
+  /* Hybrid_type operations. */
+  virtual void set_zero(Hybrid_type *val) const { val->real= 0.0; }
+  virtual void add(Hybrid_type *val, Field *f) const
+  { val->real+= f->val_real(); }
+  virtual void div(Hybrid_type *val, ulonglong u) const
+  { val->real/= ulonglong2double(u); }
+
+  virtual longlong val_int(Hybrid_type *val, bool unsigned_flag) const
+  { return (longlong) val->real; }
+  virtual double val_real(Hybrid_type *val) const { return val->real; }
+  virtual my_decimal *val_decimal(Hybrid_type *val, my_decimal *buf) const;
+  virtual String *val_str(Hybrid_type *val, String *buf, uint8 decimals) const;
+  static const Hybrid_type_traits *instance();
+};
+
+
+struct Hybrid_type_traits_decimal: public Hybrid_type_traits
+{
+  virtual Item_result type() const { return DECIMAL_RESULT; }
+
+  virtual void
+  fix_length_and_dec(Item *arg, Item *item) const;
+
+  /* Hybrid_type operations. */
+  virtual void set_zero(Hybrid_type *val) const;
+  virtual void add(Hybrid_type *val, Field *f) const;
+  virtual void div(Hybrid_type *val, ulonglong u) const;
+
+  virtual longlong val_int(Hybrid_type *val, bool unsigned_flag) const;
+  virtual double val_real(Hybrid_type *val) const;
+  virtual my_decimal *val_decimal(Hybrid_type *val, my_decimal *buf) const
+  { return &val->dec_buf[val->used_dec_buf_no]; }
+  virtual String *val_str(Hybrid_type *val, String *buf, uint8 decimals) const;
+  static const Hybrid_type_traits_decimal *instance();
+};
+
+
+struct Hybrid_type_traits_integer: public Hybrid_type_traits
+{
+  virtual Item_result type() const { return INT_RESULT; }
+
+  virtual void
+  fix_length_and_dec(Item *arg, Item *item) const;
+
+  /* Hybrid_type operations. */
+  virtual void set_zero(Hybrid_type *val) const
+  { val->integer= 0; }
+  virtual void add(Hybrid_type *val, Field *f) const
+  { val->integer+= f->val_int(); }
+  virtual void div(Hybrid_type *val, ulonglong u) const
+  { val->integer/= (longlong) u; }
+
+  virtual longlong val_int(Hybrid_type *val, bool unsigned_flag) const
+  { return val->integer; }
+  virtual double val_real(Hybrid_type *val) const
+  { return (double) val->integer; }
+  virtual my_decimal *val_decimal(Hybrid_type *val, my_decimal *buf) const
+  {
+    int2my_decimal(E_DEC_FATAL_ERROR, val->integer, 0, &val->dec_buf[2]);
+    return &val->dec_buf[2];
+  }
+  virtual String *val_str(Hybrid_type *val, String *buf, uint8 decimals) const
+  { buf->set(val->integer, &my_charset_bin); return buf;}
+  static const Hybrid_type_traits_integer *instance();
+};
+
+/*************************************************************************/
+
 typedef bool (Item::*Item_processor)(byte *arg);
 typedef Item* (Item::*Item_transformer) (byte *arg);
 

sql/item_sum.cc

@@ -456,11 +456,30 @@ my_decimal *Item_sum_sum::val_decimal(my_decimal *val)
   return val_decimal_from_real(val);
 }
 
+/***************************************************************************/
 
-/* Item_sum_sum_distinct */
+C_MODE_START
+
+/* Declarations for auxilary C-callbacks */
+
+static int simple_raw_key_cmp(void* arg, const void* key1, const void* key2)
+{
+    return memcmp(key1, key2, *(uint *) arg);
+}
+
+
+static int item_sum_distinct_walk(void *element, element_count num_of_dups,
+                                  void *item)
+{
+    return ((Item_sum_distinct*) (item))->unique_walk_function(element);
+}
+
+C_MODE_END
 
-Item_sum_sum_distinct::Item_sum_sum_distinct(Item *item)
-  :Item_sum_sum(item), tree(0)
+/* Item_sum_distinct */
+
+Item_sum_distinct::Item_sum_distinct(Item *item_arg)
+  :Item_sum_num(item_arg), tree(0)
 {
   /*
     quick_group is an optimizer hint, which means that GROUP BY can be
@@ -472,239 +491,242 @@ Item_sum_sum_distinct::Item_sum_sum_distinct(Item *item)
 }
 
 
-Item_sum_sum_distinct::Item_sum_sum_distinct(THD *thd,
-                                             Item_sum_sum_distinct *original)
-  :Item_sum_sum(thd, original), tree(0), dec_bin_buff(original->dec_bin_buff)
+Item_sum_distinct::Item_sum_distinct(THD *thd, Item_sum_distinct *original)
+  :Item_sum_num(thd, original), val(original->val), tree(0),
+  table_field_type(original->table_field_type)
 {
   quick_group= 0;
 }
 
 
-void Item_sum_sum_distinct::fix_length_and_dec()
+/*
+  Behaves like an Integer except to fix_length_and_dec().
+  Additionally div() converts val with this traits to a val with true
+  decimal traits along with conversion of integer value to decimal value.
+  This is to speedup SUM/AVG(DISTINCT) evaluation for 8-32 bit integer
+  values.
+*/
+
+struct Hybrid_type_traits_fast_decimal: public
+       Hybrid_type_traits_integer
 {
-  Item_sum_sum::fix_length_and_dec();
-  if (hybrid_type == DECIMAL_RESULT)
+  virtual Item_result type() const { return DECIMAL_RESULT; }
+  virtual void fix_length_and_dec(Item *item, Item *arg) const
+  { Hybrid_type_traits_decimal::instance()->fix_length_and_dec(item, arg); }
+
+  virtual void div(Hybrid_type *val, ulonglong u) const
   {
-    dec_bin_buff= (byte *)
-      sql_alloc(my_decimal_get_binary_size(args[0]->max_length,
-                                           args[0]->decimals));
+    int2my_decimal(E_DEC_FATAL_ERROR, val->integer, 0, val->dec_buf);
+    val->used_dec_buf_no= 0;
+    val->traits= Hybrid_type_traits_decimal::instance();
+    val->traits->div(val, u);
   }
-}
+  static const Hybrid_type_traits_fast_decimal *instance()
+  {
+    static const Hybrid_type_traits_fast_decimal fast_decimal_traits;
+    return &fast_decimal_traits;
+  }
+};
 
 
-Item *
-Item_sum_sum_distinct::copy_or_same(THD *thd)
+void Item_sum_distinct::fix_length_and_dec()
 {
-  return new (thd->mem_root) Item_sum_sum_distinct(thd, this);
-}
+  DBUG_ASSERT(args[0]->fixed);
 
-C_MODE_START
+  table_field_type= args[0]->field_type();
 
-static int simple_raw_key_cmp(void* arg, const void* key1, const void* key2)
-{
-  return memcmp(key1, key2, *(uint *) arg);
+  /* Adjust tmp table type according to the chosen aggregation type */
+  switch (args[0]->result_type()) {
+  case STRING_RESULT:
+  case REAL_RESULT:
+    val.traits= Hybrid_type_traits::instance();
+    if (table_field_type != MYSQL_TYPE_FLOAT)
+      table_field_type= MYSQL_TYPE_DOUBLE;
+    break;
+  case INT_RESULT:
+  /*
+    Preserving int8, int16, int32 field types gives ~10% performance boost
+    as the size of result tree becomes significantly smaller.
+    Another speed up we gain by using longlong for intermediate
+    calculations. The range of int64 is enough to hold sum 2^32 distinct
+    integers each <= 2^32.
+  */
+  if (table_field_type == MYSQL_TYPE_INT24 ||
+      table_field_type >= MYSQL_TYPE_TINY &&
+      table_field_type <= MYSQL_TYPE_LONG)
+  {
+    val.traits= Hybrid_type_traits_fast_decimal::instance();
+    break;
+  }
+  table_field_type= MYSQL_TYPE_LONGLONG;
+  /* fallthrough */
+  case DECIMAL_RESULT:
+    val.traits= Hybrid_type_traits_decimal::instance();
+    if (table_field_type != MYSQL_TYPE_LONGLONG)
+      table_field_type= MYSQL_TYPE_NEWDECIMAL;
+    break;
+  case ROW_RESULT:
+  default:
+    DBUG_ASSERT(0);
+  }
+  val.traits->fix_length_and_dec(this, args[0]);
 }
 
-C_MODE_END
-
 
-bool Item_sum_sum_distinct::setup(THD *thd)
+bool Item_sum_distinct::setup(THD *thd)
 {
-  DBUG_ENTER("Item_sum_sum_distinct::setup");
-  SELECT_LEX *select_lex= thd->lex->current_select;
-  /* what does it mean??? */
-  if (select_lex->linkage == GLOBAL_OPTIONS_TYPE)
-    DBUG_RETURN(1);
+  List<create_field> field_list;
+  create_field field_def;                              /* field definition */
+
+  DBUG_ENTER("Item_sum_distinct::setup");
 
   DBUG_ASSERT(tree == 0);                 /* setup can not be called twice */
 
   /*
-    Uniques handles all unique elements in a tree until they can't fit in.
-    Then thee tree is dumped to the temporary file.
-    See class Unique for details.
+    Virtual table and the tree are created anew on each re-execution of
+    PS/SP. Hence all further allocations are performed in the runtime
+    mem_root.
   */
+  if (field_list.push_back(&field_def))
+    return TRUE;
+
   null_value= maybe_null= 1;
-  /*
-    TODO: if underlying item result fits in 4 bytes we can take advantage
-    of it and have tree of long/ulong. It gives 10% performance boost
-  */
+  quick_group= 0;
+
+  DBUG_ASSERT(args[0]->fixed);
+
+  field_def.init_for_tmp_table(table_field_type, args[0]->max_length,
+                               args[0]->decimals, args[0]->maybe_null,
+                               args[0]->unsigned_flag);
+
+  if (! (table= create_virtual_tmp_table(thd, field_list)))
+      return TRUE;
+
+  /* XXX: check that the case of CHAR(0) works OK */
+  tree_key_length= table->s->reclength - table->s->null_bytes;
 
   /*
-    It's safe to use key_length here as even if we do copy_or_same()
-    the new item will just share the old items key_length, which will not
-    change or disappear during the life time of this item.
+    Unique handles all unique elements in a tree until they can't fit
+    in.  Then the tree is dumped to the temporary file. We can use
+    simple_raw_key_cmp because the table contains numbers only; decimals
+    are converted to binary representation as well.
   */
-  key_length= ((hybrid_type == DECIMAL_RESULT) ?
-               my_decimal_get_binary_size(args[0]->max_length,
-                                          args[0]->decimals) :
-               sizeof(double));
-  tree= new Unique(simple_raw_key_cmp, &key_length, key_length,
+  tree= new Unique(simple_raw_key_cmp, &tree_key_length, tree_key_length,
                    thd->variables.max_heap_table_size);
-  DBUG_PRINT("info", ("tree 0x%lx, key length %d", (ulong)tree,
-                      key_length));
-  DBUG_RETURN(tree == 0);
-}
-
-void Item_sum_sum_distinct::clear()
-{
-  DBUG_ENTER("Item_sum_sum_distinct::clear");
-  DBUG_ASSERT(tree != 0);                        /* we always have a tree */
-  null_value= 1; 
-  tree->reset();
-  DBUG_VOID_RETURN;
-}
 
-void Item_sum_sum_distinct::cleanup()
-{
-  Item_sum_num::cleanup();
-  delete tree;
-  tree= 0;
+  DBUG_RETURN(tree == 0);
 }
 
 
-bool Item_sum_sum_distinct::add()
+bool Item_sum_distinct::add()
 {
-  DBUG_ENTER("Item_sum_sum_distinct::add");
-  if (hybrid_type == DECIMAL_RESULT)
+  args[0]->save_in_field(table->field[0], FALSE);
+  if (!table->field[0]->is_null())
   {
-    my_decimal value, *val= args[0]->val_decimal(&value);
-    if (!args[0]->null_value)
-    {
-      DBUG_ASSERT(tree != 0);
-      null_value= 0;
-      my_decimal2binary(E_DEC_FATAL_ERROR, val, (char *) dec_bin_buff,
-                        args[0]->max_length, args[0]->decimals);
-      DBUG_RETURN(tree->unique_add(dec_bin_buff));
-    }
-  }
-  else
-  {
-    /* args[0]->val() may reset args[0]->null_value */
-    double val= args[0]->val_real();
-    if (!args[0]->null_value)
-    {
-      DBUG_ASSERT(tree != 0);
-      null_value= 0;
-      DBUG_PRINT("info", ("real: %lg, tree 0x%lx", val, (ulong)tree));
-      if (val)
-        DBUG_RETURN(tree->unique_add(&val));
-    }
-    else
-      DBUG_PRINT("info", ("real: NULL"));
+    DBUG_ASSERT(tree);
+    null_value= 0;
+    /*
+      '0' values are also stored in the tree. This doesn't matter
+      for SUM(DISTINCT), but is important for AVG(DISTINCT)
+    */
+    return tree->unique_add(table->field[0]->ptr);
   }
-  DBUG_RETURN(0);
+  return 0;
 }
 
 
-void Item_sum_sum_distinct::add_real(double val)
+bool Item_sum_distinct::unique_walk_function(void *element)
 {
-  DBUG_ENTER("Item_sum_sum_distinct::add_real");
-  sum+= val;
-  DBUG_PRINT("info", ("sum %lg, val %lg", sum, val));
-  DBUG_VOID_RETURN;
+  memcpy(table->field[0]->ptr, element, tree_key_length);
+  ++count;
+  val.traits->add(&val, table->field[0]);
+  return 0;
 }
 
 
-void Item_sum_sum_distinct::add_decimal(byte *val)
+void Item_sum_distinct::clear()
 {
-  binary2my_decimal(E_DEC_FATAL_ERROR, (char *) val, &tmp_dec,
-                    args[0]->max_length, args[0]->decimals);
-  my_decimal_add(E_DEC_FATAL_ERROR, dec_buffs + (curr_dec_buff^1),
-                 &tmp_dec, dec_buffs + curr_dec_buff);
-  curr_dec_buff^= 1;
+  DBUG_ENTER("Item_sum_distinct::clear");
+  DBUG_ASSERT(tree != 0);                        /* we always have a tree */
+  null_value= 1;
+  tree->reset();
+  DBUG_VOID_RETURN;
 }
 
-C_MODE_START
-
-static int sum_sum_distinct_real(void *element, element_count num_of_dups,
-                                 void *item_sum_sum_distinct)
-{ 
-  ((Item_sum_sum_distinct *)
-   (item_sum_sum_distinct))->add_real(* (double *) element);
-  return 0;
+void Item_sum_distinct::cleanup()
+{
+  Item_sum_num::cleanup();
+  delete tree;
+  tree= 0;
+  table= 0;
 }
 
-static int sum_sum_distinct_decimal(void *element, element_count num_of_dups,
-                                    void *item_sum_sum_distinct)
-{ 
-  ((Item_sum_sum_distinct *)
-   (item_sum_sum_distinct))->add_decimal((byte *)element);
-  return 0;
+Item_sum_distinct::~Item_sum_distinct()
+{
+  delete tree;
+  /* no need to free the table */
 }
 
-C_MODE_END
-
 
-double Item_sum_sum_distinct::val_real()
+void Item_sum_distinct::calculate_val_and_count()
 {
-  DBUG_ENTER("Item_sum_sum_distinct::val");
+  count= 0;
+  val.traits->set_zero(&val);
   /*
     We don't have a tree only if 'setup()' hasn't been called;
     this is the case of sql_select.cc:return_zero_rows.
   */
-  if (hybrid_type == DECIMAL_RESULT)
+  if (tree)
   {
-    /* Item_sum_sum_distinct::val_decimal do not use argument */
-    my_decimal *val= val_decimal(0);
-    if (!null_value)
-      my_decimal2double(E_DEC_FATAL_ERROR, val, &sum);
-  }
-  else
-  {
-    sum= 0.0;
-    DBUG_PRINT("info", ("tree 0x%lx", (ulong)tree));
-    if (tree) 
-      tree->walk(sum_sum_distinct_real, (void *) this);
+    table->field[0]->set_notnull();
+    tree->walk(item_sum_distinct_walk, (void*) this);
   }
-  DBUG_RETURN(sum);
 }
 
 
-my_decimal *Item_sum_sum_distinct::val_decimal(my_decimal *fake)
+double Item_sum_distinct::val_real()
 {
-  if (hybrid_type == DECIMAL_RESULT)
-  {
-    my_decimal_set_zero(dec_buffs);
-    curr_dec_buff= 0;
-    if (tree)
-      tree->walk(sum_sum_distinct_decimal, (void *)this);
-  }
-  else
-  {
-    double real= val_real();
-    curr_dec_buff= 0;
-    double2my_decimal(E_DEC_FATAL_ERROR, real, dec_buffs);
-  }
-  return(dec_buffs + curr_dec_buff);
+  calculate_val_and_count();
+  return val.traits->val_real(&val);
 }
 
 
-longlong Item_sum_sum_distinct::val_int()
+my_decimal *Item_sum_distinct::val_decimal(my_decimal *to)
 {
-  longlong result;
-  if (hybrid_type == DECIMAL_RESULT)
-  {
-    /* Item_sum_sum_distinct::val_decimal do not use argument */
-    my_decimal *val= val_decimal(0);
-    if (!null_value)
-      my_decimal2int(E_DEC_FATAL_ERROR, val, unsigned_flag, &result);
-  }
-  else
-    result= (longlong) val_real();
-  return result;
+  calculate_val_and_count();
+  if (null_value)
+    return 0;
+  return val.traits->val_decimal(&val, to);
 }
 
 
-String *Item_sum_sum_distinct::val_str(String *str)
+longlong Item_sum_distinct::val_int()
 {
-  DBUG_ASSERT(fixed == 1);
-  if (hybrid_type == DECIMAL_RESULT)
-    return val_string_from_decimal(str);
-  return val_string_from_real(str);
+  calculate_val_and_count();
+  return val.traits->val_int(&val, unsigned_flag);
 }
 
 
-/* end of Item_sum_sum_distinct */
+String *Item_sum_distinct::val_str(String *str)
+{
+  calculate_val_and_count();
+  if (null_value)
+    return 0;
+  return val.traits->val_str(&val, str, decimals);
+}
+
+/* end of Item_sum_distinct */
+
+/* Item_sum_avg_distinct */
+
+void
+Item_sum_avg_distinct::calculate_val_and_count()
+{
+  Item_sum_distinct::calculate_val_and_count();
+  if (count)
+    val.traits->div(&val, count);
+}
+
 
 Item *Item_sum_count::copy_or_same(THD* thd)
 {

sql/item_sum.h

@@ -30,8 +30,8 @@ class Item_sum :public Item_result_field
 public:
   enum Sumfunctype
   { COUNT_FUNC, COUNT_DISTINCT_FUNC, SUM_FUNC, SUM_DISTINCT_FUNC, AVG_FUNC,
-    MIN_FUNC, MAX_FUNC, UNIQUE_USERS_FUNC, STD_FUNC, VARIANCE_FUNC,
-    SUM_BIT_FUNC, UDF_SUM_FUNC, GROUP_CONCAT_FUNC
+    AVG_DISTINCT_FUNC, MIN_FUNC, MAX_FUNC, UNIQUE_USERS_FUNC, STD_FUNC,
+    VARIANCE_FUNC, SUM_BIT_FUNC, UDF_SUM_FUNC, GROUP_CONCAT_FUNC
   };
 
   Item **args, *tmp_args[2];
@@ -68,6 +68,9 @@ public:
     a temporary table. Similar to reset(), but must also store value in
     result_field. Like reset() it is supposed to reset start value to
     default.
+    This set of methods (reult_field(), reset_field, update_field()) of
+    Item_sum is used only if quick_group is not null. Otherwise
+    copy_or_same() is used to obtain a copy of this item.
   */
   virtual void reset_field()=0;
   /*
@@ -161,26 +164,28 @@ public:
 };
 
 
-/*
-  Item_sum_sum_distinct - SELECT SUM(DISTINCT expr) FROM ... 
-  support. See also: MySQL manual, chapter 'Adding New Functions To MySQL'
-  and comments in item_sum.cc.
-*/
+
+/* Common class for SUM(DISTINCT), AVG(DISTINCT) */
 
 class Unique;
 
-class Item_sum_sum_distinct :public Item_sum_sum
+class Item_sum_distinct :public Item_sum_num
 {
+protected:
+  /* storage for the summation result */
+  ulonglong count;
+  Hybrid_type val;
+  /* storage for unique elements */
   Unique *tree;
-  byte *dec_bin_buff;
-  my_decimal tmp_dec;
-  uint key_length;
-private:
-  Item_sum_sum_distinct(THD *thd, Item_sum_sum_distinct *item);
+  TABLE *table;
+  enum enum_field_types table_field_type;
+  uint tree_key_length;
+protected:
+  Item_sum_distinct(THD *thd, Item_sum_distinct *item);
 public:
-  Item_sum_sum_distinct(Item *item_par);
-  ~Item_sum_sum_distinct() {}
-  
+  Item_sum_distinct(Item *item_par);
+  ~Item_sum_distinct();
+
   bool setup(THD *thd);
   void clear();
   void cleanup();
@@ -190,15 +195,54 @@ public:
   longlong val_int();
   String *val_str(String *str);
 
-  void add_real(double val);
-  void add_decimal(byte *val);
+  /* XXX: does it need make_unique? */
+
   enum Sumfunctype sum_func () const { return SUM_DISTINCT_FUNC; }
   void reset_field() {} // not used
   void update_field() {} // not used
   const char *func_name() const { return "sum_distinct"; }
-  Item *copy_or_same(THD* thd);
   virtual void no_rows_in_result() {}
   void fix_length_and_dec();
+  enum Item_result result_type () const { return val.traits->type(); }
+  virtual void calculate_val_and_count();
+  virtual bool unique_walk_function(void *elem);
+};
+
+
+/*
+  Item_sum_sum_distinct - implementation of SUM(DISTINCT expr).
+  See also: MySQL manual, chapter 'Adding New Functions To MySQL'
+  and comments in item_sum.cc.
+*/
+
+class Item_sum_sum_distinct :public Item_sum_distinct
+{
+private:
+  Item_sum_sum_distinct(THD *thd, Item_sum_sum_distinct *item)
+    :Item_sum_distinct(thd, item) {}
+public:
+  Item_sum_sum_distinct(Item *item_arg) :Item_sum_distinct(item_arg) {}
+
+  enum Sumfunctype sum_func () const { return SUM_DISTINCT_FUNC; }
+  const char *func_name() const { return "sum_distinct"; }
+  Item *copy_or_same(THD* thd) { return new Item_sum_sum_distinct(thd, this); }
+};
+
+
+/* Item_sum_avg_distinct - SELECT AVG(DISTINCT expr) FROM ... */
+
+class Item_sum_avg_distinct: public Item_sum_distinct
+{
+private:
+  Item_sum_avg_distinct(THD *thd, Item_sum_avg_distinct *original)
+    :Item_sum_distinct(thd, original) {}
+public:
+  Item_sum_avg_distinct(Item *item_arg) : Item_sum_distinct(item_arg) {}
+
+  virtual void calculate_val_and_count();
+  enum Sumfunctype sum_func () const { return AVG_DISTINCT_FUNC; }
+  const char *func_name() const { return "avg_distinct"; }
+  Item *copy_or_same(THD* thd) { return new Item_sum_avg_distinct(thd, this); }
 };
 
 

sql/sql_select.cc

@@ -8359,6 +8359,117 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
 }
 
 
+/****************************************************************************/
+
+/*
+  Create a reduced TABLE object with properly set up Field list from a
+  list of field definitions.
+
+  SYNOPSIS
+    create_virtual_tmp_table()
+      thd         connection handle
+      field_list  list of column definitions
+
+  DESCRIPTION
+    The created table doesn't have a table handler assotiated with
+    it, has no keys, no group/distinct, no copy_funcs array.
+    The sole purpose of this TABLE object is to use the power of Field
+    class to read/write data to/from table->record[0]. Then one can store
+    the record in any container (RB tree, hash, etc).
+    The table is created in THD mem_root, so are the table's fields.
+    Consequently, if you don't BLOB fields, you don't need to free it.
+
+  RETURN
+    0 if out of memory, TABLE object in case of success
+*/
+
+TABLE *create_virtual_tmp_table(THD *thd, List<create_field> &field_list)
+{
+  uint field_count= field_list.elements;
+  Field **field;
+  create_field *cdef;                           /* column definition */
+  uint record_length= 0;
+  uint null_count= 0;                 /* number of columns which may be null */
+  uint null_pack_length;              /* NULL representation array length */
+  TABLE_SHARE *s;
+  /* Create the table and list of all fields */
+  TABLE *table= (TABLE*) thd->calloc(sizeof(*table));
+  field= (Field**) thd->alloc((field_count + 1) * sizeof(Field*));
+  if (!table || !field)
+    return 0;
+
+  table->field= field;
+  table->s= s= &table->share_not_to_be_used;
+  s->fields= field_count;
+
+  /* Create all fields and calculate the total length of record */
+  List_iterator_fast<create_field> it(field_list);
+  while ((cdef= it++))
+  {
+    *field= make_field(0, cdef->length,
+                       (uchar*) (f_maybe_null(cdef->pack_flag) ? "" : 0),
+                       f_maybe_null(cdef->pack_flag) ? 1 : 0,
+                       cdef->pack_flag, cdef->sql_type, cdef->charset,
+                       cdef->geom_type, cdef->unireg_check,
+                       cdef->interval, cdef->field_name, table);
+    if (!*field)
+      goto error;
+    record_length+= (**field).pack_length();
+    if (! ((**field).flags & NOT_NULL_FLAG))
+      ++null_count;
+    ++field;
+  }
+  *field= NULL;                                 /* mark the end of the list */
+
+  null_pack_length= (null_count + 7)/8;
+  s->reclength= record_length + null_pack_length;
+  s->rec_buff_length= ALIGN_SIZE(s->reclength + 1);
+  table->record[0]= (byte*) thd->alloc(s->rec_buff_length);
+  if (!table->record[0])
+    goto error;
+
+  if (null_pack_length)
+  {
+    table->null_flags= (uchar*) table->record[0];
+    s->null_fields= null_count;
+    s->null_bytes= null_pack_length;
+  }
+
+  table->in_use= thd;           /* field->reset() may access table->in_use */
+  {
+    /* Set up field pointers */
+    byte *null_pos= table->record[0];
+    byte *field_pos= null_pos + s->null_bytes;
+    uint null_bit= 1;
+
+    for (field= table->field; *field; ++field)
+    {
+      Field *cur_field= *field;
+      if ((cur_field->flags & NOT_NULL_FLAG))
+        cur_field->move_field((char*) field_pos);
+      else
+      {
+        cur_field->move_field((char*) field_pos, (uchar*) null_pos, null_bit);
+        null_bit<<= 1;
+        if (null_bit == (1 << 8))
+        {
+          ++null_pos;
+          null_bit= 1;
+        }
+      }
+      cur_field->reset();
+
+      field_pos+= cur_field->pack_length();
+    }
+  }
+  return table;
+error:
+  for (field= table->field; *field; ++field)
+    delete *field;                         /* just invokes field destructor */
+  return 0;
+}
+
+
 static bool open_tmp_table(TABLE *table)
 {
   int error;

sql/sql_select.h

@@ -387,6 +387,7 @@ TABLE *create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
 			ORDER *group, bool distinct, bool save_sum_fields,
 			ulong select_options, ha_rows rows_limit,
 			char* alias);
+TABLE *create_virtual_tmp_table(THD *thd, List<create_field> &field_list);
 void free_tmp_table(THD *thd, TABLE *entry);
 void count_field_types(TMP_TABLE_PARAM *param, List<Item> &fields,
 		       bool reset_with_sum_func);

sql/sql_yacc.yy

@@ -4754,6 +4754,8 @@ udf_expr:
 sum_expr:
 	AVG_SYM '(' in_sum_expr ')'
 	  { $$=new Item_sum_avg($3); }
+	| AVG_SYM '(' DISTINCT in_sum_expr ')'
+	  { $$=new Item_sum_avg_distinct($4); }
 	| BIT_AND  '(' in_sum_expr ')'
 	  { $$=new Item_sum_and($3); }
 	| BIT_OR  '(' in_sum_expr ')'