WL#1724 "Min/Max Optimization for Queries with Group By Clause"

- after-review changes
- merged with the source tree from 204-08-27

mysql-test/r/distinct.result

@@ -200,19 +200,19 @@ select distinct 1 from t1,t3 where t1.a=t3.a;
 1
 explain SELECT distinct t1.a from t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	range	NULL	PRIMARY	4	NULL	5	Using index for group-by
 explain SELECT distinct t1.a from t1 order by a desc;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	range	NULL	PRIMARY	4	NULL	5	Using index for group-by; Using temporary; Using filesort
 explain SELECT t1.a from t1 group by a order by a desc;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	range	NULL	PRIMARY	4	NULL	5	Using index for group-by; Using temporary; Using filesort
 explain SELECT distinct t1.a from t1 order by a desc limit 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	5	Using index
 explain SELECT distinct a from t3 order by a desc limit 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	index	NULL	a	5	NULL	204	Using index
+1	SIMPLE	t3	index	NULL	a	5	NULL	10	Using index
 explain SELECT distinct a,b from t3 order by a+1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	204	Using temporary; Using filesort

sql/ha_myisam.cc

@@ -1515,7 +1515,8 @@ longlong ha_myisam::get_auto_increment()
   int error;
   byte key[MI_MAX_KEY_LENGTH];
   (void) extra(HA_EXTRA_KEYREAD);
-  key_copy(key,table,table->next_number_index,
+  key_copy(key, table->record[0],
+           table->key_info + table->next_number_index,
            table->next_number_key_offset);
   error=mi_rkey(file,table->record[1],(int) table->next_number_index,
 		key,table->next_number_key_offset,HA_READ_PREFIX_LAST);

sql/handler.cc

@@ -984,7 +984,8 @@ longlong handler::get_auto_increment()
   else
   {
     byte key[MAX_KEY_LENGTH];
-    key_copy(key,table,table->next_number_index,
+    key_copy(key, table->record[0],
+             table->key_info + table->next_number_index,
              table->next_number_key_offset);
     error=index_read(table->record[1], key, table->next_number_key_offset,
                      HA_READ_PREFIX_LAST);

sql/item.cc

@@ -159,6 +159,46 @@ bool Item_ident::remove_dependence_processor(byte * arg)
 }
 
 
+/*
+  Store the pointer to this item field into a list if not already there.
+
+  SYNOPSIS
+    Item_field::collect_item_field_processor()
+    arg  pointer to a List<Item_field>
+
+  DESCRIPTION
+    The method is used by Item::walk to collect all unique Item_field objects
+    from a tree of Items into a set of items represented as a list.
+
+  IMPLEMENTATION
+    Item_cond::walk() and Item_func::walk() stop the evaluation of the
+    processor function for its arguments once the processor returns
+    true.Therefore in order to force this method being called for all item
+    arguments in a condition the method must return false.
+
+  RETURN
+    false on success (force the evaluation of collect_item_field_processor
+          for the subsequent items.)
+    true  o/w (stop evaluation of subsequent items.)
+*/
+
+bool Item_field::collect_item_field_processor(byte *arg)
+{
+  DBUG_ENTER("Item_field::collect_item_field_processor");
+  DBUG_PRINT("info", ("%s", field->field_name ? field->field_name : "noname"));
+  List<Item_field> *item_list= (List<Item_field>*) arg;
+  List_iterator<Item_field> item_list_it(*item_list);
+  Item_field *curr_item;
+  while ((curr_item= item_list_it++))
+  {
+    if (curr_item->eq(this, 1))
+      DBUG_RETURN(false); /* Already in the set. */
+  }
+  item_list->push_back(this);
+  DBUG_RETURN(false);
+}
+
+
 bool Item::check_cols(uint c)
 {
   if (c != 1)

sql/item.h

@@ -260,6 +260,22 @@ class Item {
 
   virtual bool remove_dependence_processor(byte * arg) { return 0; }
   virtual bool remove_fixed(byte * arg) { fixed= 0; return 0; }
+  /*
+    All collect_* methods are used as arguments to walk() to collect
+    specific types items.
+    TODO:
+    A more generic implementation would add a special class
+    Collect_processor_param that can store arbitrary sets of item kinds
+    (currently specified as enums), along with a list to store items of the
+    specified kinds. This would allow to collect combinations of items of
+    arbitrary kinds without having to add a new collect method each time.
+    There can be one generic collect_processor method that checks the item type
+    and compares it with the item types in Collect_processor_param.
+  */
+  virtual bool collect_item_field_processor(byte * arg) { return 0; }
+  virtual bool collect_item_sum_min_processor(byte * arg) { return 0; }
+  virtual bool collect_item_sum_max_processor(byte * arg) { return 0; }
+  virtual bool has_non_min_max_sum_processor(byte * arg) { return 0; }
   
   virtual Item *this_item() { return this; } /* For SPs mostly. */
   virtual Item *this_const_item() const { return const_cast<Item*>(this); } /* For SPs mostly. */
@@ -493,6 +509,7 @@ class Item_field :public Item_ident
   bool get_time(TIME *ltime);
   bool is_null() { return field->is_null(); }
   Item *get_tmp_table_item(THD *thd);
+  bool collect_item_field_processor(byte * arg);
   void cleanup();
   inline uint32 max_disp_length() { return field->max_length(); }
   friend class Item_default_value;
@@ -984,6 +1001,8 @@ class Item_ref :public Item_ident
     (*ref)->save_in_field(result_field, no_conversions);
   }
   Item *real_item() { return *ref; }
+  bool walk(Item_processor processor, byte *arg)
+  { return (*ref)->walk(processor, arg); }
   void print(String *str);
   void cleanup();
 };

sql/item_sum.cc

@@ -182,6 +182,45 @@ bool Item_sum::walk (Item_processor processor, byte *argument)
   return (this->*processor)(argument);
 }
 
+
+/*
+  Store the pointer to this item into a list if not already there.
+
+  SYNOPSIS
+    Item_sum::collect()
+    item_list  pointer to a List<Item_sum> where item_sum objects are collected
+
+  DESCRIPTION
+    The method is used by collect_item_sum_*_processor, called by
+    Item_sum::walk, to collect all unique Item_sum_min and Item_sum_max objects
+    from a tree of Items into a set of items represented as a list.
+
+  IMPLEMENTATION
+    Item_cond::walk() and Item_func::walk() stop the evaluation of the
+    processor function for its arguments once the processor returns
+    true.Therefore in order to force this method being called for all item
+    arguments in a condition the method must return false.
+
+  RETURN
+    FALSE on success (force the evaluation of collect_item_sum_*_processor
+          for the subsequent items.)
+    TRUE  o/w (stop evaluation of subsequent items.)
+*/
+
+bool Item_sum::collect(List<Item_sum> *item_list)
+{
+  List_iterator<Item_sum> item_list_it(*item_list);
+  Item_sum *curr_item;
+  while ((curr_item= item_list_it++))
+  {
+    if (curr_item == this)
+      return FALSE; /* Already in the set. */
+  }
+  item_list->push_back(this);
+  return FALSE;
+}
+
+
 String *
 Item_sum_num::val_str(String *str)
 {

sql/item_sum.h

@@ -27,6 +27,8 @@ class Item_arena;
 
 class Item_sum :public Item_result_field
 {
+private:
+  bool collect(List<Item_sum> *item_list);
 public:
   enum Sumfunctype
   { COUNT_FUNC, COUNT_DISTINCT_FUNC, SUM_FUNC, SUM_DISTINCT_FUNC, AVG_FUNC,
@@ -98,6 +100,33 @@ class Item_sum :public Item_result_field
   bool save_args(Item_arena* stmt);
 
   bool walk (Item_processor processor, byte *argument);
+
+  /* Collect Item_sum_min objects into a list supplied by the caller. */
+  bool collect_item_sum_min_processor(byte *arg)
+  {
+    if (Item_sum::MIN_FUNC == this->sum_func())
+      return collect((List<Item_sum>*) arg);
+    else
+      return FALSE;
+  }
+
+  /* Collect Item_sum_max objects into a list supplied by the caller. */
+  bool collect_item_sum_max_processor(byte *arg)
+  {
+    if (Item_sum::MAX_FUNC == this->sum_func())
+      return collect((List<Item_sum>*) arg);
+    else
+      return FALSE;
+   }
+
+  /* Check if there are any aggregate functions other than MIN and MAX. */
+  bool has_non_min_max_sum_processor(byte * arg)
+  {
+    Sumfunctype sum_type= this->sum_func();
+    if ((sum_type != Item_sum::MIN_FUNC) && (sum_type != Item_sum::MAX_FUNC))
+      return TRUE;
+    return FALSE;
+  }
 };
 
 

sql/key.cc

@@ -66,94 +66,121 @@ int find_ref_key(TABLE *table,Field *field, uint *key_length)
 }
 
 
-	/* Copy a key from record to some buffer */
-	/* if length == 0 then copy whole key */
+/*
+  Copy part of a record that forms a key or key prefix to a buffer.
+
+  SYNOPSIS
+    key_copy()
+    to_key      buffer that will be used as a key
+    from_record full record to be copied from
+    key_info    descriptor of the index
+    key_length  specifies length of all keyparts that will be copied
+
+  DESCRIPTION
+    The function takes a complete table record (as e.g. retrieved by
+    handler::index_read()), and a description of an index on the same table,
+    and extracts the first key_length bytes of the record which are part of a
+    key into to_key. If length == 0 then copy all bytes from the record that
+    form a key.
+
+  RETURN
+    None
+*/
 
-void key_copy(byte *key,TABLE *table,uint idx,uint key_length)
+void key_copy(byte *to_key, byte *from_record, KEY *key_info, uint key_length)
 {
   uint length;
-  KEY *key_info=table->key_info+idx;
   KEY_PART_INFO *key_part;
 
   if (key_length == 0)
-    key_length=key_info->key_length;
-  for (key_part=key_info->key_part;
-       (int) key_length > 0 ;
-       key_part++)
+    key_length= key_info->key_length;
+  for (key_part= key_info->key_part; (int) key_length > 0; key_part++)
   {
     if (key_part->null_bit)
     {
-      *key++= test(table->record[0][key_part->null_offset] &
+      *to_key++= test(from_record[key_part->null_offset] &
 		   key_part->null_bit);
       key_length--;
     }
     if (key_part->key_part_flag & HA_BLOB_PART)
     {
       char *pos;
-      ulong blob_length=((Field_blob*) key_part->field)->get_length();
-      key_length-=2;
+      ulong blob_length= ((Field_blob*) key_part->field)->get_length();
+      key_length-= 2;
       ((Field_blob*) key_part->field)->get_ptr(&pos);
-      length=min(key_length,key_part->length);
-      set_if_smaller(blob_length,length);
-      int2store(key,(uint) blob_length);
-      key+=2;					// Skip length info
-      memcpy(key,pos,blob_length);
+      length=min(key_length, key_part->length);
+      set_if_smaller(blob_length, length);
+      int2store(to_key, (uint) blob_length);
+      to_key+= 2;					// Skip length info
+      memcpy(to_key, pos, blob_length);
     }
     else
     {
-      length=min(key_length,key_part->length);
-      memcpy(key,table->record[0]+key_part->offset,(size_t) length);
+      length= min(key_length, key_part->length);
+      memcpy(to_key, from_record + key_part->offset, (size_t) length);
     }
-    key+=length;
-    key_length-=length;
+    to_key+= length;
+    key_length-= length;
   }
-} /* key_copy */
+}
 
 
-	/* restore a key from some buffer to record */
+/*
+  Restore a key from some buffer to record.
+
+  SYNOPSIS
+    key_restore()
+    to_record   record buffer where the key will be restored to
+    from_key    buffer that contains a key
+    key_info    descriptor of the index
+    key_length  specifies length of all keyparts that will be restored
+
+  DESCRIPTION
+    This function converts a key into record format. It can be used in cases
+    when we want to return a key as a result row.
+
+  RETURN
+    None
+*/
 
-void key_restore(TABLE *table,byte *key,uint idx,uint key_length)
+void key_restore(byte *to_record, byte *from_key, KEY *key_info,
+                 uint key_length)
 {
   uint length;
-  KEY *key_info=table->key_info+idx;
   KEY_PART_INFO *key_part;
 
   if (key_length == 0)
   {
-    if (idx == (uint) -1)
-      return;
-    key_length=key_info->key_length;
+    key_length= key_info->key_length;
   }
-  for (key_part=key_info->key_part;
-       (int) key_length > 0 ;
-       key_part++)
+  for (key_part= key_info->key_part ; (int) key_length > 0 ; key_part++)
   {
     if (key_part->null_bit)
     {
-      if (*key++)
-	table->record[0][key_part->null_offset]|= key_part->null_bit;
+      if (*from_key++)
+	to_record[key_part->null_offset]|= key_part->null_bit;
       else
-	table->record[0][key_part->null_offset]&= ~key_part->null_bit;
+	to_record[key_part->null_offset]&= ~key_part->null_bit;
       key_length--;
     }
     if (key_part->key_part_flag & HA_BLOB_PART)
     {
-      uint blob_length=uint2korr(key);
-      key+=2;
-      key_length-=2;
+      uint blob_length= uint2korr(from_key);
+      from_key+= 2;
+      key_length-= 2;
       ((Field_blob*) key_part->field)->set_ptr((ulong) blob_length,
-					       (char*) key);
-      length=key_part->length;
+					       (char*) from_key);
+      length= key_part->length;
     }
     else
     {
-      length=min(key_length,key_part->length);
-      memcpy(table->record[0]+key_part->offset,key,(size_t) length);
+      length= min(key_length, key_part->length);
+      memcpy(to_record + key_part->offset, from_key, (size_t) length);
     }
-    key+=length;
-    key_length-=length;
+    from_key+= length;
+    key_length-= length;
   }
-} /* key_restore */
+}
 
 
 /*

sql/mysql_priv.h

@@ -733,7 +733,8 @@ bool add_proc_to_list(THD *thd, Item *item);
 TABLE *unlink_open_table(THD *thd,TABLE *list,TABLE *find);
 
 SQL_SELECT *make_select(TABLE *head, table_map const_tables,
-			table_map read_tables, COND *conds, int *error);
+			table_map read_tables, COND *conds, int *error,
+                        bool allow_null_cond= false);
 enum find_item_error_report_type {REPORT_ALL_ERRORS, REPORT_EXCEPT_NOT_FOUND,
 				  IGNORE_ERRORS};
 extern const Item **not_found_item;
@@ -814,8 +815,9 @@ void print_plan(JOIN* join, double read_time, double record_count,
 void mysql_print_status(THD *thd);
 /* key.cc */
 int find_ref_key(TABLE *form,Field *field, uint *offset);
-void key_copy(byte *key,TABLE *form,uint index,uint key_length);
-void key_restore(TABLE *form,byte *key,uint index,uint key_length);
+void key_copy(byte *to_key, byte *from_record, KEY *key_info, uint key_length);
+void key_restore(byte *to_record, byte *from_key, KEY *key_info,
+                 uint key_length);
 bool key_cmp_if_same(TABLE *form,const byte *key,uint index,uint key_length);
 void key_unpack(String *to,TABLE *form,uint index);
 bool check_if_key_used(TABLE *table, uint idx, List<Item> &fields);

sql/opt_range.h

@@ -146,7 +146,8 @@ class QUICK_SELECT_I
     QS_TYPE_RANGE_DESC = 2,
     QS_TYPE_FULLTEXT   = 3,
     QS_TYPE_ROR_INTERSECT = 4,
-    QS_TYPE_ROR_UNION = 5
+    QS_TYPE_ROR_UNION = 5,
+    QS_TYPE_GROUP_MIN_MAX = 6
   };
 
   /* Get type of this quick select - one of the QS_TYPE_* values */
@@ -278,14 +279,12 @@ class QUICK_RANGE_SELECT : public QUICK_SELECT_I
   int init();
   int get_next();
   void range_end();
-
+  int get_next_prefix(uint prefix_length, byte *cur_prefix);
   bool reverse_sorted() { return 0; }
   bool unique_key_range();
   int init_ror_merged_scan(bool reuse_handler);
   void save_last_pos()
-  {
-    file->position(record);
-  };
+  { file->position(record); }
   int get_type() { return QS_TYPE_RANGE; }
   void add_keys_and_lengths(String *key_names, String *used_lengths);
   void add_info_string(String *str);
@@ -518,6 +517,103 @@ class QUICK_ROR_UNION_SELECT : public QUICK_SELECT_I
 };
 
 
+/*
+  Index scan for GROUP-BY queries with MIN/MAX aggregate functions.
+
+  This class provides a specialized index access method for GROUP-BY queries
+  of the forms:
+
+       SELECT A_1,...,A_k, [B_1,...,B_m], [MIN(C)], [MAX(C)]
+         FROM T
+        WHERE [RNG(A_1,...,A_p ; where p <= k)]
+         [AND EQ(B_1,...,B_m)]
+         [AND PC(C)]
+         [AND PA(A_i1,...,A_iq)]
+       GROUP BY A_1,...,A_k;
+
+    or
+
+       SELECT DISTINCT A_i1,...,A_ik
+         FROM T
+        WHERE [RNG(A_1,...,A_p ; where p <= k)]
+         [AND PA(A_i1,...,A_iq)];
+
+  where all selected fields are parts of the same index.
+  The class of queries that can be processed by this quick select is fully
+  specified in the description of get_best_trp_group_min_max() in opt_range.cc.
+
+  The get_next() method directly produces result tuples, thus obviating the
+  need to call end_send_group() because all grouping is already done inside
+  get_next().
+
+  Since one of the requirements is that all select fields are part of the same
+  index, this class produces only index keys, and not complete records.
+*/
+
+class QUICK_GROUP_MIN_MAX_SELECT : public QUICK_SELECT_I
+{
+private:
+  handler *file;         /* The handler used to get data. */
+  JOIN *join;            /* Descriptor of the current query */
+  KEY  *index_info;      /* The index chosen for data access */
+  byte *record;          /* Buffer where the next record is returned. */
+  byte *tmp_record;      /* Temporary storage for next_min(), next_max(). */
+  byte *group_prefix;    /* Key prefix consisting of the GROUP fields. */
+  uint group_prefix_len; /* Length of the group prefix. */
+  byte *last_prefix;     /* Prefix of the last group for detecting EOF. */
+  bool have_min;         /* Specify whether we are computing */
+  bool have_max;         /*   a MIN, a MAX, or both.         */
+  bool seen_first_key;   /* Denotes whether the first key was retrieved.*/
+  KEY_PART_INFO *min_max_arg_part; /* The keypart of the only argument field */
+                                   /* of all MIN/MAX functions.              */
+  uint min_max_arg_len;  /* The length of the MIN/MAX argument field */
+  byte *key_infix;       /* Infix of constants from equality predicates. */
+  uint key_infix_len;
+  DYNAMIC_ARRAY min_max_ranges; /* Array of range ptrs for the MIN/MAX field. */
+  uint real_prefix_len; /* Length of key prefix extended with key_infix. */
+  List<Item_sum> *min_functions;
+  List<Item_sum> *max_functions;
+  List_iterator<Item_sum> *min_functions_it;
+  List_iterator<Item_sum> *max_functions_it;
+public:
+  /*
+    The following two members are public to allow easy access from
+    TRP_GROUP_MIN_MAX::make_quick()
+  */
+  MEM_ROOT alloc; /* Memory pool for this and quick_prefix_select data. */
+  QUICK_RANGE_SELECT *quick_prefix_select;/* For retrieval of group prefixes. */
+private:
+  int  next_prefix();
+  int  next_min_in_range();
+  int  next_max_in_range();
+  int  next_min();
+  int  next_max();
+  void update_min_result();
+  void update_max_result();
+public:
+  QUICK_GROUP_MIN_MAX_SELECT(TABLE *table, JOIN *join, bool have_min,
+                             bool have_max, KEY_PART_INFO *min_max_arg_part,
+                             uint group_prefix_len, uint used_key_parts,
+                             KEY *index_info, uint use_index, double read_cost,
+                             ha_rows records, uint key_infix_len,
+                             byte *key_infix, MEM_ROOT *parent_alloc);
+  ~QUICK_GROUP_MIN_MAX_SELECT();
+  bool add_range(SEL_ARG *sel_range);
+  void update_key_stat();
+  bool alloc_buffers();
+  int init();
+  int reset();
+  int get_next();
+  bool reverse_sorted() { return false; }
+  bool unique_key_range() { return false; }
+  int get_type() { return QS_TYPE_GROUP_MIN_MAX; }
+  void add_keys_and_lengths(String *key_names, String *used_lengths);
+#ifndef DBUG_OFF
+  void dbug_dump(int indent, bool verbose);
+#endif
+};
+
+
 class QUICK_SELECT_DESC: public QUICK_RANGE_SELECT
 {
 public:

sql/opt_sum.cc

@@ -336,7 +336,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
     1        Otherwise
 */
 
-static bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
+bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
 {
   Item *item;
   *inv_order= 0;

sql/sql_acl.cc

@@ -1884,7 +1884,7 @@ GRANT_TABLE::GRANT_TABLE(TABLE *form, TABLE *col_privs)
              col_privs->field[1]->pack_length()+
              col_privs->field[2]->pack_length()+
              col_privs->field[3]->pack_length());
-    key_copy(key,col_privs,0,key_len);
+    key_copy(key,col_privs->record[0],col_privs->key_info,key_len);
     col_privs->field[4]->store("",0, &my_charset_latin1);
     col_privs->file->ha_index_init(0);
     if (col_privs->file->index_read(col_privs->record[0],
@@ -1996,7 +1996,7 @@ static int replace_column_table(GRANT_TABLE *g_t,
   table->field[3]->store(table_name,(uint) strlen(table_name), &my_charset_latin1);
   key_length=(table->field[0]->pack_length()+ table->field[1]->pack_length()+
 	      table->field[2]->pack_length()+ table->field[3]->pack_length());
-  key_copy(key,table,0,key_length);
+  key_copy(key,table->record[0],table->key_info,key_length);
 
   rights &= COL_ACLS;				// Only ACL for columns
 
@@ -2009,7 +2009,7 @@ static int replace_column_table(GRANT_TABLE *g_t,
   {
     ulong privileges = xx->rights;
     bool old_row_exists=0;
-    key_restore(table,key,0,key_length);
+    key_restore(table->record[0],key,table->key_info,key_length);
     table->field[4]->store(xx->column.ptr(),xx->column.length(),
                            &my_charset_latin1);
 
@@ -2025,7 +2025,7 @@ static int replace_column_table(GRANT_TABLE *g_t,
       }
       old_row_exists = 0;
       restore_record(table,default_values);		// Get empty record
-      key_restore(table,key,0,key_length);
+      key_restore(table->record[0],key,table->key_info,key_length);
       table->field[4]->store(xx->column.ptr(),xx->column.length(),
                              &my_charset_latin1);
     }

sql/sql_handler.cc

@@ -333,7 +333,7 @@ int mysql_ha_read(THD *thd, TABLE_LIST *tables,
 	send_error(thd,ER_OUTOFMEMORY);
 	goto err;
       }
-      key_copy(key, table, keyno, key_len);
+      key_copy(key, table->record[0], table->key_info + keyno, key_len);
       err=table->file->index_read(table->record[0],
 				  key,key_len,ha_rkey_mode);
       mode=rkey_to_rnext[(int)ha_rkey_mode];

sql/sql_insert.cc

@@ -635,7 +635,7 @@ int write_record(TABLE *table,COPY_INFO *info)
 	    goto err;
 	  }
 	}
-	key_copy((byte*) key,table,key_nr,0);
+	key_copy((byte*) key,table->record[0],table->key_info+key_nr,0);
 	if ((error=(table->file->index_read_idx(table->record[1],key_nr,
 						(byte*) key,
 						table->key_info[key_nr].

sql/sql_select.cc

@@ -188,6 +188,7 @@ static bool update_sum_func(Item_sum **func);
 static void select_describe(JOIN *join, bool need_tmp_table,bool need_order,
 			    bool distinct, const char *message=NullS);
 static Item *remove_additional_cond(Item* conds);
+static void add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab);
 
 
 /*
@@ -635,7 +636,7 @@ JOIN::optimize()
     conds=new Item_int((longlong) 1,1);	// Always true
   }
   select=make_select(*table, const_table_map,
-		     const_table_map, conds, &error);
+		     const_table_map, conds, &error, true);
   if (error)
   {						/* purecov: inspected */
     error= -1;					/* purecov: inspected */
@@ -2304,6 +2305,12 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
     if (s->worst_seeks < 2.0)			// Fix for small tables
       s->worst_seeks=2.0;
 
+    /*
+      Add to stat->const_keys those indexes for which all group fields or
+      all select distinct fields participate in one index.
+    */
+    add_group_and_distinct_keys(join, s);
+
     if (!s->const_keys.is_clear_all() &&
         !s->table->pos_in_table_list->embedding)
     {
@@ -2312,7 +2319,9 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
       select= make_select(s->table, found_const_table_map,
 			  found_const_table_map,
 			  s->on_expr ? s->on_expr : conds,
-			  &error);
+			  &error, true);
+      if (!select)
+        DBUG_RETURN(1);
       records= get_quick_record_count(join->thd, select, s->table,
 				      &s->const_keys, join->row_limit);
       s->quick=select->quick;
@@ -2347,13 +2356,13 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
     }
   }
 
-  /* Find best combination and return it */
   join->join_tab=stat;
   join->map2table=stat_ref;
   join->table= join->all_tables=table_vector;
   join->const_tables=const_count;
   join->found_const_table_map=found_const_table_map;
 
+  /* Find an optimal join order of the non-constant tables. */
   if (join->const_tables != join->tables)
   {
     optimize_keyuse(join, keyuse_array);
@@ -2365,6 +2374,7 @@ make_join_statistics(JOIN *join,TABLE_LIST *tables,COND *conds,
 	   sizeof(POSITION)*join->const_tables);
     join->best_read=1.0;
   }
+  /* Generate an execution plan from the found optimal join order. */
   DBUG_RETURN(join->thd->killed || get_best_combination(join));
 }
 
@@ -2561,6 +2571,10 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, COND *cond,
 
       bool is_const=1;
       for (uint i=0; i<num_values; i++)
+        /*
+          TODO: this looks like a bug, should be
+          is_const&= (value[i])->const_item();
+        */
         is_const&= (*value)->const_item();
       if (is_const)
         stat[0].const_keys.merge(possible_keys);
@@ -2997,6 +3011,68 @@ static void optimize_keyuse(JOIN *join, DYNAMIC_ARRAY *keyuse_array)
 }
 
 
+/*
+  Discover the indexes that can be used for GROUP BY or DISTINCT queries.
+
+  SYNOPSIS
+    add_group_and_distinct_keys()
+    join
+    join_tab
+
+  DESCRIPTION
+    If the query has a GROUP BY clause, find all indexes that contain all
+    GROUP BY fields, and add those indexes to join->const_keys.
+    If the query has a DISTINCT clause, find all indexes that contain all
+    SELECT fields, and add those indexes to join->const_keys.
+    This allows later on such queries to be processed by a
+    QUICK_GROUP_MIN_MAX_SELECT.
+
+  RETURN
+    None
+*/
+
+static void
+add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab)
+{
+  List<Item_field> indexed_fields;
+  List_iterator<Item_field> indexed_fields_it(indexed_fields);
+  ORDER      *cur_group;
+  Item_field *cur_item;
+  key_map possible_keys(0);
+
+  if (join->group_list)
+  { /* Collect all query fields referenced in the GROUP clause. */
+    for (cur_group= join->group_list; cur_group; cur_group= cur_group->next)
+      (*cur_group->item)->walk(&Item::collect_item_field_processor,
+                               (byte*) &indexed_fields);
+  }
+  else if (join->select_distinct)
+  { /* Collect all query fields referenced in the SELECT clause. */
+    List<Item> &select_items= join->fields_list;
+    List_iterator<Item> select_items_it(select_items);
+    Item *item;
+    while ((item= select_items_it++))
+      item->walk(&Item::collect_item_field_processor, (byte*) &indexed_fields);
+  }
+  else
+    return;
+
+  if (indexed_fields.elements == 0)
+    return;
+
+  /* Intersect the keys of all group fields. */
+  cur_item= indexed_fields_it++;
+  possible_keys.merge(cur_item->field->part_of_key);
+  while ((cur_item= indexed_fields_it++))
+  {
+    possible_keys.intersect(cur_item->field->part_of_key);
+  }
+
+  if (!possible_keys.is_clear_all())
+    join_tab->const_keys.merge(possible_keys);
+}
+
+
 /*****************************************************************************
   Go through all combinations of not marked tables and find the one
   which uses least records
@@ -4883,6 +4959,8 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
   if (select)
   {
     table_map used_tables;
+    if (cond)                /* Because of QUICK_GROUP_MIN_MAX_SELECT */
+    {                        /* there may be a select without a cond. */
       if (join->tables > 1)
         cond->update_used_tables();		// Tablenr may have changed
       if (join->const_tables == join->tables &&
@@ -4899,6 +4977,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
           DBUG_RETURN(1);				// Impossible const condition
         }
       }
+    }
     used_tables=((select->const_tables=join->const_table_map) |
 		 OUTER_REF_TABLE_BIT | RAND_TABLE_BIT);
     for (uint i=join->const_tables ; i < join->tables ; i++)
@@ -4928,8 +5007,10 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	join->best_positions[i].records_read= rows2double(tab->quick->records);
       }
 
-      COND *tmp=make_cond_for_table(cond,used_tables,current_map);
-      if (!tmp && tab->quick)
+      COND *tmp= NULL;
+      if (cond)
+        tmp= make_cond_for_table(cond,used_tables,current_map);
+      if (cond && !tmp && tab->quick)
       {						// Outer join
 	/*
 	  Hack to handle the case where we only refer to a table
@@ -4937,8 +5018,9 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	*/
 	tmp=new Item_int((longlong) 1,1);	// Always true
       }
-      if (tmp)
+      if (tmp || !cond)
       {
+        if (tmp)
           DBUG_EXECUTE("where",print_where(tmp,tab->table->table_name););
 	SQL_SELECT *sel=tab->select=(SQL_SELECT*)
 	  join->thd->memdup((gptr) select, sizeof(SQL_SELECT));
@@ -4950,9 +5032,17 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
           The guard will turn the predicate on only after
           the first match for outer tables is encountered.
 	*/
+        if (cond)
+        {/*
+            Because of QUICK_GROUP_MIN_MAX_SELECT there may be a select without
+            a cond, so neutralize the hack above.
+          */
           if (!(tmp= add_found_match_trig_cond(first_inner_tab, tmp, 0)))
             DBUG_RETURN(1);
           tab->select_cond=sel->cond=tmp;
+        }
+        else
+          tab->select_cond= sel->cond= NULL;
 
 	sel->head=tab->table;
 	if (tab->quick)
@@ -4992,7 +5082,8 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	    the index if we are using limit and this is the first table
 	  */
 
-	  if ((!tab->keys.is_subset(tab->const_keys) && i > 0) ||
+	  if (cond &&
+              (!tab->keys.is_subset(tab->const_keys) && i > 0) ||
 	      (!tab->const_keys.is_clear_all() && i == join->const_tables &&
 	       join->unit->select_limit_cnt <
 	       join->best_positions[i].records_read &&
@@ -5050,7 +5141,8 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	  }
 	  if (i != join->const_tables && tab->use_quick != 2)
 	  {					/* Read with cache */
-	    if ((tmp=make_cond_for_table(cond,
+	    if (cond &&
+                (tmp=make_cond_for_table(cond,
 					 join->const_table_map |
 					 current_map,
 					 current_map)))
@@ -7444,11 +7536,18 @@ do_select(JOIN *join,List<Item> *fields,TABLE *table,Procedure *procedure)
   }
   else
   {
-    if (join->sort_and_group || (join->procedure &&
-				 join->procedure->flags & PROC_GROUP))
-      end_select=end_send_group;
+    /* Test if data is accessed via QUICK_GROUP_MIN_MAX_SELECT. */
+    bool is_using_quick_group_min_max_select=
+      (join->join_tab->select && join->join_tab->select->quick &&
+       (join->join_tab->select->quick->get_type() ==
+        QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX));
+
+    if ((join->sort_and_group ||
+         (join->procedure && join->procedure->flags & PROC_GROUP)) &&
+        !is_using_quick_group_min_max_select)
+      end_select= end_send_group;
     else
-      end_select=end_send;
+      end_select= end_send;
   }
   join->join_tab[join->tables-1].next_select=end_select;
 
@@ -9225,7 +9324,8 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
                   & HA_READ_PREV) ||
                 quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE ||
                 quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT ||
-                quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION)
+                quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION ||
+                quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
               DBUG_RETURN(0);			// Use filesort
             
             /* ORDER BY range_key DESC */
@@ -11455,11 +11555,16 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
             extra.append(tab->keys.print(buf));
             extra.append(')');
 	  }
-	  else
+	  else if (tab->select->cond)
             extra.append("; Using where");
 	}
 	if (key_read)
+        {
+          if (quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+            extra.append("; Using index for group-by");
+          else
             extra.append("; Using index");
+        }
 	if (table->reginfo.not_exists_optimize)
 	  extra.append("; Not exists");
 	if (need_tmp_table)

sql/sql_select.h

@@ -399,6 +399,7 @@ bool create_myisam_from_heap(THD *thd, TABLE *table, TMP_TABLE_PARAM *param,
 uint find_shortest_key(TABLE *table, const key_map *usable_keys);
 
 /* functions from opt_sum.cc */
+bool simple_pred(Item_func *func_item, Item **args, bool *inv_order);
 int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds);
 
 /* from sql_delete.cc, used by opt_range.cc */