path: root/sql/item_sum.h

#ifndef ITEM_SUM_INCLUDED
#define ITEM_SUM_INCLUDED
/* Copyright (c) 2000, 2011 Oracle and/or its affiliates.
   Copyright (c) 2008, 2013 Monty Program Ab.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */


/* classes for sum functions */

#ifdef USE_PRAGMA_INTERFACE
#pragma interface			/* gcc class implementation */
#endif

#include <my_tree.h>
#include "sql_udf.h"                            /* udf_handler */

class Item_sum;
class Aggregator_distinct;
class Aggregator_simple;

/**
  The abstract base class for the Aggregator_* classes.
  It implements the data collection functions (setup/add/clear)
  as either pass-through to the real functionality or
  as collectors into an Unique (for distinct) structure.

  Note that update_field/reset_field are not in that
  class, because they're simply not called when
  GROUP BY/DISTINCT can be handled with help of index on grouped 
  fields (quick_group = 0);
*/

class Aggregator : public Sql_alloc
{
  friend class Item_sum;
  friend class Item_sum_sum;
  friend class Item_sum_count;
  friend class Item_sum_avg;

  /* 
    All members are protected as this class is not usable outside of an 
    Item_sum descendant.
  */
protected:
  /* the aggregate function class to act on */
  Item_sum *item_sum;

  /**
    When feeding back the data in endup() from Unique/temp table back to
    Item_sum::add() methods we must read the data from Unique (and not 
    recalculate the functions that are given as arguments to the aggregate
    function. 
    This flag is to tell the add() methods to take the data from the Unique
    instead by calling the relevant val_..() method
  */

  bool use_distinct_values;

public:
  Aggregator (Item_sum *arg): item_sum(arg), use_distinct_values(FALSE) {}
  virtual ~Aggregator () {}                   /* Keep gcc happy */

  enum Aggregator_type { SIMPLE_AGGREGATOR, DISTINCT_AGGREGATOR }; 
  virtual Aggregator_type Aggrtype() = 0;

  /**
    Called before adding the first row. 
    Allocates and sets up the internal aggregation structures used, 
    e.g. the Unique instance used to calculate distinct.
  */
  virtual bool setup(THD *) = 0;

  /**
    Called when we need to wipe out all the data from the aggregator :
    all the values acumulated and all the state.
    Cleans up the internal structures and resets them to their initial state.
  */
  virtual void clear() = 0;

  /**
    Called when there's a new value to be aggregated.
    Updates the internal state of the aggregator to reflect the new value.
  */
  virtual bool add() = 0;

  /**
    Called when there are no more data and the final value is to be retrieved.
    Finalises the state of the aggregator, so the final result can be retrieved.
  */
  virtual void endup() = 0;

  /** Decimal value of being-aggregated argument */
  virtual my_decimal *arg_val_decimal(my_decimal * value) = 0;
  /** Floating point value of being-aggregated argument */
  virtual double arg_val_real() = 0;
  /**
     NULLness of being-aggregated argument; can be called only after
     arg_val_decimal() or arg_val_real().
  */
  virtual bool arg_is_null() = 0;
};


class st_select_lex;

/**
  Class Item_sum is the base class used for special expressions that SQL calls
  'set functions'. These expressions are formed with the help of aggregate
  functions such as SUM, MAX, GROUP_CONCAT etc.

 GENERAL NOTES

  A set function cannot be used in certain positions where expressions are
  accepted. There are some quite explicable restrictions for the usage of 
  set functions.

  In the query:
    SELECT AVG(b) FROM t1 WHERE SUM(b) > 20 GROUP by a
  the usage of the set function AVG(b) is legal, while the usage of SUM(b)
  is illegal. A WHERE condition must contain expressions that can be 
  evaluated for each row of the table. Yet the expression SUM(b) can be
  evaluated only for each group of rows with the same value of column a.
  In the query:
    SELECT AVG(b) FROM t1 WHERE c > 30 GROUP BY a HAVING SUM(b) > 20
  both set function expressions AVG(b) and SUM(b) are legal.

  We can say that in a query without nested selects an occurrence of a
  set function in an expression of the SELECT list or/and in the HAVING
  clause is legal, while in the WHERE clause it's illegal.

  The general rule to detect whether a set function is legal in a query with
  nested subqueries is much more complicated.

  Consider the the following query:
    SELECT t1.a FROM t1 GROUP BY t1.a
      HAVING t1.a > ALL (SELECT t2.c FROM t2 WHERE SUM(t1.b) < t2.c).
  The set function SUM(b) is used here in the WHERE clause of the subquery.
  Nevertheless it is legal since it is under the HAVING clause of the query
  to which this function relates. The expression SUM(t1.b) is evaluated
  for each group defined in the main query, not for groups of the subquery.

  The problem of finding the query where to aggregate a particular
  set function is not so simple as it seems to be.

  In the query: 
    SELECT t1.a FROM t1 GROUP BY t1.a
     HAVING t1.a > ALL(SELECT t2.c FROM t2 GROUP BY t2.c
                         HAVING SUM(t1.a) < t2.c)
  the set function can be evaluated for both outer and inner selects.
  If we evaluate SUM(t1.a) for the outer query then we get the value of t1.a
  multiplied by the cardinality of a group in table t1. In this case 
  in each correlated subquery SUM(t1.a) is used as a constant. But we also
  can evaluate SUM(t1.a) for the inner query. In this case t1.a will be a
  constant for each correlated subquery and summation is performed
  for each group of table t2.
  (Here it makes sense to remind that the query
    SELECT c FROM t GROUP BY a HAVING SUM(1) < a 
  is quite legal in our SQL).

  So depending on what query we assign the set function to we
  can get different result sets.

  The general rule to detect the query where a set function is to be
  evaluated can be formulated as follows.
  Consider a set function S(E) where E is an expression with occurrences
  of column references C1, ..., CN. Resolve these column references against
  subqueries that contain the set function S(E). Let Q be the innermost
  subquery of those subqueries. (It should be noted here that S(E)
  in no way can be evaluated in the subquery embedding the subquery Q,
  otherwise S(E) would refer to at least one unbound column reference)
  If S(E) is used in a construct of Q where set functions are allowed then
  we evaluate S(E) in Q.
  Otherwise we look for a innermost subquery containing S(E) of those where
  usage of S(E) is allowed.

  Let's demonstrate how this rule is applied to the following queries.

  1. SELECT t1.a FROM t1 GROUP BY t1.a
       HAVING t1.a > ALL(SELECT t2.b FROM t2 GROUP BY t2.b
                           HAVING t2.b > ALL(SELECT t3.c FROM t3 GROUP BY t3.c
                                                HAVING SUM(t1.a+t2.b) < t3.c))
  For this query the set function SUM(t1.a+t2.b) depends on t1.a and t2.b
  with t1.a defined in the outermost query, and t2.b defined for its
  subquery. The set function is in the HAVING clause of the subquery and can
  be evaluated in this subquery.

  2. SELECT t1.a FROM t1 GROUP BY t1.a
       HAVING t1.a > ALL(SELECT t2.b FROM t2
                           WHERE t2.b > ALL (SELECT t3.c FROM t3 GROUP BY t3.c
                                               HAVING SUM(t1.a+t2.b) < t3.c))
  Here the set function SUM(t1.a+t2.b)is in the WHERE clause of the second
  subquery - the most upper subquery where t1.a and t2.b are defined.
  If we evaluate the function in this subquery we violate the context rules.
  So we evaluate the function in the third subquery (over table t3) where it
  is used under the HAVING clause.

  3. SELECT t1.a FROM t1 GROUP BY t1.a
       HAVING t1.a > ALL(SELECT t2.b FROM t2
                           WHERE t2.b > ALL (SELECT t3.c FROM t3 
                                               WHERE SUM(t1.a+t2.b) < t3.c))
  In this query evaluation of SUM(t1.a+t2.b) is not legal neither in the second
  nor in the third subqueries. So this query is invalid.

  Mostly set functions cannot be nested. In the query
    SELECT t1.a from t1 GROUP BY t1.a HAVING AVG(SUM(t1.b)) > 20
  the expression SUM(b) is not acceptable, though it is under a HAVING clause.
  Yet it is acceptable in the query:
    SELECT t.1 FROM t1 GROUP BY t1.a HAVING SUM(t1.b) > 20.

  An argument of a set function does not have to be a reference to a table
  column as we saw it in examples above. This can be a more complex expression
    SELECT t1.a FROM t1 GROUP BY t1.a HAVING SUM(t1.b+1) > 20.
  The expression SUM(t1.b+1) has a very clear semantics in this context:
  we sum up the values of t1.b+1 where t1.b varies for all values within a
  group of rows that contain the same t1.a value.

  A set function for an outer query yields a constant within a subquery. So
  the semantics of the query
    SELECT t1.a FROM t1 GROUP BY t1.a
      HAVING t1.a IN (SELECT t2.c FROM t2 GROUP BY t2.c
                        HAVING AVG(t2.c+SUM(t1.b)) > 20)
  is still clear. For a group of the rows with the same t1.a values we
  calculate the value of SUM(t1.b). This value 's' is substituted in the
  the subquery:
    SELECT t2.c FROM t2 GROUP BY t2.c HAVING AVG(t2.c+s)
  than returns some result set.

  By the same reason the following query with a subquery 
    SELECT t1.a FROM t1 GROUP BY t1.a
      HAVING t1.a IN (SELECT t2.c FROM t2 GROUP BY t2.c
                        HAVING AVG(SUM(t1.b)) > 20)
  is also acceptable.

 IMPLEMENTATION NOTES

  Three methods were added to the class to check the constraints specified
  in the previous section. These methods utilize several new members.

  The field 'nest_level' contains the number of the level for the subquery
  containing the set function. The main SELECT is of level 0, its subqueries
  are of levels 1, the subqueries of the latter are of level 2 and so on.

  The field 'aggr_level' is to contain the nest level of the subquery
  where the set function is aggregated.

  The field 'max_arg_level' is for the maximun of the nest levels of the
  unbound column references occurred in the set function. A column reference
  is unbound  within a set function if it is not bound by any subquery
  used as a subexpression in this function. A column reference is bound by
  a subquery if it is a reference to the column by which the aggregation
  of some set function that is used in the subquery is calculated.
  For the set function used in the query
    SELECT t1.a FROM t1 GROUP BY t1.a
      HAVING t1.a > ALL(SELECT t2.b FROM t2 GROUP BY t2.b
                          HAVING t2.b > ALL(SELECT t3.c FROM t3 GROUP BY t3.c
                                              HAVING SUM(t1.a+t2.b) < t3.c))
  the value of max_arg_level is equal to 1 since t1.a is bound in the main
  query, and t2.b is bound by the first subquery whose nest level is 1.
  Obviously a set function cannot be aggregated in the subquery whose
  nest level is less than max_arg_level. (Yet it can be aggregated in the
  subqueries whose nest level is greater than max_arg_level.)
  In the query
    SELECT t.a FROM t1 HAVING AVG(t1.a+(SELECT MIN(t2.c) FROM t2))
  the value of the max_arg_level for the AVG set function is 0 since
  the reference t2.c is bound in the subquery.

  The field 'max_sum_func_level' is to contain the maximum of the
  nest levels of the set functions that are used as subexpressions of
  the arguments of the given set function, but not aggregated in any
  subquery within this set function. A nested set function s1 can be
  used within set function s0 only if s1.max_sum_func_level <
  s0.max_sum_func_level. Set function s1 is considered as nested
  for set function s0 if s1 is not calculated in any subquery
  within s0.

  A set function that is used as a subexpression in an argument of another
  set function refers to the latter via the field 'in_sum_func'.

  The condition imposed on the usage of set functions are checked when
  we traverse query subexpressions with the help of the recursive method
  fix_fields. When we apply this method to an object of the class
  Item_sum, first, on the descent, we call the method init_sum_func_check
  that initialize members used at checking. Then, on the ascent, we
  call the method check_sum_func that validates the set function usage
  and reports an error if it is illegal.
  The method register_sum_func serves to link the items for the set functions
  that are aggregated in the embedding (sub)queries. Circular chains of such
  functions are attached to the corresponding st_select_lex structures
  through the field inner_sum_func_list.

  Exploiting the fact that the members mentioned above are used in one
  recursive function we could have allocated them on the thread stack.
  Yet we don't do it now.
  
  We assume that the nesting level of subquries does not exceed 127.
  TODO: to catch queries where the limit is exceeded to make the
  code clean here.  
    
*/

class Item_sum :public Item_result_field
{
  friend class Aggregator_distinct;
  friend class Aggregator_simple;

protected:
  /**
    Aggregator class instance. Not set initially. Allocated only after
    it is determined if the incoming data are already distinct.
  */
  Aggregator *aggr;

private:
  /**
    Used in making ROLLUP. Set for the ROLLUP copies of the original
    Item_sum and passed to create_tmp_field() to cause it to work
    over the temp table buffer that is referenced by
    Item_result_field::result_field.
  */
  bool force_copy_fields;

  /**
    Indicates how the aggregate function was specified by the parser :
    1 if it was written as AGGREGATE(DISTINCT),
    0 if it was AGGREGATE()
  */
  bool with_distinct;

public:

  bool has_force_copy_fields() const { return force_copy_fields; }
  bool has_with_distinct()     const { return with_distinct; }

  enum Sumfunctype
  { COUNT_FUNC, COUNT_DISTINCT_FUNC, SUM_FUNC, SUM_DISTINCT_FUNC, AVG_FUNC,
    AVG_DISTINCT_FUNC, MIN_FUNC, MAX_FUNC, STD_FUNC,
    VARIANCE_FUNC, SUM_BIT_FUNC, UDF_SUM_FUNC, GROUP_CONCAT_FUNC
  };

  Item **ref_by; /* pointer to a ref to the object used to register it */
  Item_sum *next; /* next in the circular chain of registered objects  */
  Item_sum *in_sum_func;  /* embedding set function if any */ 
  st_select_lex * aggr_sel; /* select where the function is aggregated       */ 
  int8 nest_level;        /* number of the nesting level of the set function */
  int8 aggr_level;        /* nesting level of the aggregating subquery       */
  int8 max_arg_level;     /* max level of unbound column references          */
  int8 max_sum_func_level;/* max level of aggregation for embedded functions */
  bool quick_group;			/* If incremental update of fields */
  /*
    This list is used by the check for mixing non aggregated fields and
    sum functions in the ONLY_FULL_GROUP_BY_MODE. We save all outer fields
    directly or indirectly used under this function it as it's unclear
    at the moment of fixing outer field whether it's aggregated or not.
  */
  List<Item_field> outer_fields;

protected:  
  uint arg_count;
  Item **args, *tmp_args[2];
  /* 
    Copy of the arguments list to hold the original set of arguments.
    Used in EXPLAIN EXTENDED instead of the current argument list because 
    the current argument list can be altered by usage of temporary tables.
  */
  Item **orig_args, *tmp_orig_args[2];
  table_map used_tables_cache;
  
  /*
    TRUE <=> We've managed to calculate the value of this Item in
    opt_sum_query(), hence it can be considered constant at all subsequent
    steps.
  */
  bool forced_const;
  static ulonglong ram_limitation(THD *thd);

public:  

  void mark_as_sum_func();
  Item_sum() :quick_group(1), arg_count(0), forced_const(FALSE)
  {
    mark_as_sum_func();
    init_aggregator();
  }
  Item_sum(Item *a) :quick_group(1), arg_count(1), args(tmp_args),
    orig_args(tmp_orig_args), forced_const(FALSE)
  {
    args[0]=a;
    mark_as_sum_func();
    init_aggregator();
  }
  Item_sum( Item *a, Item *b ) :quick_group(1), arg_count(2), args(tmp_args),
    orig_args(tmp_orig_args), forced_const(FALSE)
  {
    args[0]=a; args[1]=b;
    mark_as_sum_func();
    init_aggregator();
  }
  Item_sum(List<Item> &list);
  //Copy constructor, need to perform subselects with temporary tables
  Item_sum(THD *thd, Item_sum *item);
  enum Type type() const { return SUM_FUNC_ITEM; }
  virtual enum Sumfunctype sum_func () const=0;
  /**
    Resets the aggregate value to its default and aggregates the current
    value of its attribute(s).
  */  
  inline bool reset_and_add() 
  { 
    aggregator_clear(); 
    return aggregator_add(); 
  };

  /*
    Called when new group is started and results are being saved in
    a temporary table. Similarly to reset_and_add() it resets the 
    value to its default and aggregates the value of its 
    attribute(s), but must also store it in result_field. 
    This set of methods (result_item(), 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;
  /*
    Called for each new value in the group, when temporary table is in use.
    Similar to add(), but uses temporary table field to obtain current value,
    Updated value is then saved in the 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; }
  virtual Item *result_item(Field *field)
    { return new Item_field(field); }
  /*
    Return bitmap of tables that are needed to evaluate the item.

    The implementation takes into account the used strategy: items resolved
    at optimization phase will report 0.
    Items that depend on the number of join output records, but not columns
    of any particular table (like COUNT(*)) will report 0 from used_tables(),
    but will still return false from const_item().
  */
  table_map used_tables() const { return used_tables_cache; }
  void update_used_tables ();
  bool is_null() { return null_value; }
  void make_const () 
  { 
    used_tables_cache= 0; 
    forced_const= TRUE; 
  }
  virtual bool const_item() const { return forced_const; }
  virtual bool const_during_execution() const { return false; }
  virtual void print(String *str, enum_query_type query_type);
  void fix_num_length_and_dec();

  /**
    Mark an aggregate as having no rows.

    This function is called by the execution engine to assign 'NO ROWS
    FOUND' value to an aggregate item, when the underlying result set
    has no rows. Such value, in a general case, may be different from
    the default value of the item after 'clear()': e.g. a numeric item
    may be initialized to 0 by clear() and to NULL by
    no_rows_in_result().
  */
  virtual void no_rows_in_result()
  {
    set_aggregator(with_distinct ?
                   Aggregator::DISTINCT_AGGREGATOR :
                   Aggregator::SIMPLE_AGGREGATOR);
    aggregator_clear();
  }
  virtual void make_unique() { force_copy_fields= TRUE; }
  Item *get_tmp_table_item(THD *thd);
  virtual Field *create_tmp_field(bool group, TABLE *table,
                                  uint convert_blob_length);
  bool walk(Item_processor processor, bool walk_subquery, uchar *argument);
  virtual bool collect_outer_ref_processor(uchar *param);
  bool init_sum_func_check(THD *thd);
  bool check_sum_func(THD *thd, Item **ref);
  bool register_sum_func(THD *thd, Item **ref);
  st_select_lex *depended_from() 
    { return (nest_level == aggr_level ? 0 : aggr_sel); }

  Item *get_arg(uint i) { return args[i]; }
  Item *set_arg(uint i, THD *thd, Item *new_val);
  uint get_arg_count() { return arg_count; }

  /* Initialization of distinct related members */
  void init_aggregator()
  {
    aggr= NULL;
    with_distinct= FALSE;
    force_copy_fields= FALSE;
  }

  /**
    Called to initialize the aggregator.
  */

  inline bool aggregator_setup(THD *thd) { return aggr->setup(thd); };

  /**
    Called to cleanup the aggregator.
  */

  inline void aggregator_clear() { aggr->clear(); }

  /**
    Called to add value to the aggregator.
  */

  inline bool aggregator_add() { return aggr->add(); };

  /* stores the declared DISTINCT flag (from the parser) */
  void set_distinct(bool distinct)
  {
    with_distinct= distinct;
    quick_group= with_distinct ? 0 : 1;
  }

  /*
    Set the type of aggregation : DISTINCT or not.

    May be called multiple times.
  */

  int set_aggregator(Aggregator::Aggregator_type aggregator);

  virtual void clear()= 0;
  virtual bool add()= 0;
  virtual bool setup(THD *thd) { return false; }

  virtual void cleanup();
  bool check_vcol_func_processor(uchar *int_arg) 
  {
    return trace_unsupported_by_check_vcol_func_processor(func_name()); 
  }
};


class Unique;


/**
 The distinct aggregator. 
 Implements AGGFN (DISTINCT ..)
 Collects all the data into an Unique (similarly to what Item_sum_distinct 
 does currently) and then (if applicable) iterates over the list of 
 unique values and pumps them back into its object
*/

class Aggregator_distinct : public Aggregator
{
  friend class Item_sum_sum;

  /* 
    flag to prevent consecutive runs of endup(). Normally in endup there are 
    expensive calculations (like walking the distinct tree for example) 
    which we must do only once if there are no data changes.
    We can re-use the data for the second and subsequent val_xxx() calls.
    endup_done set to TRUE also means that the calculated values for
    the aggregate functions are correct and don't need recalculation.
  */
  bool endup_done;

  /*
    Used depending on the type of the aggregate function and the presence of
    blob columns in it:
    - For COUNT(DISTINCT) and no blob fields this points to a real temporary
      table. It's used as a hash table.
    - For AVG/SUM(DISTINCT) or COUNT(DISTINCT) with blob fields only the
      in-memory data structure of a temporary table is constructed.
      It's used by the Field classes to transform data into row format.
  */
  TABLE *table;
  
  /*
    An array of field lengths on row allocated and used only for 
    COUNT(DISTINCT) with multiple columns and no blobs. Used in 
    Aggregator_distinct::composite_key_cmp (called from Unique to compare 
    nodes
  */
  uint32 *field_lengths;

  /*
    Used in conjunction with 'table' to support the access to Field classes 
    for COUNT(DISTINCT). Needed by copy_fields()/copy_funcs().
  */
  TMP_TABLE_PARAM *tmp_table_param;
  
  /*
    If there are no blobs in the COUNT(DISTINCT) arguments, we can use a tree,
    which is faster than heap table. In that case, we still use the table
    to help get things set up, but we insert nothing in it. 
    For AVG/SUM(DISTINCT) we always use this tree (as it takes a single 
    argument) to get the distinct rows.
  */
  Unique *tree;

  /* 
    The length of the temp table row. Must be a member of the class as it
    gets passed down to simple_raw_key_cmp () as a compare function argument
    to Unique. simple_raw_key_cmp () is used as a fast comparison function 
    when the entire row can be binary compared.
  */  
  uint tree_key_length;

  /* 
    Set to true if the result is known to be always NULL.
    If set deactivates creation and usage of the temporary table (in the 
    'table' member) and the Unique instance (in the 'tree' member) as well as 
    the calculation of the final value on the first call to 
    Item_[sum|avg|count]::val_xxx(). 
  */
  bool always_null;

public:
  Aggregator_distinct (Item_sum *sum) :
    Aggregator(sum), table(NULL), tmp_table_param(NULL), tree(NULL),
    always_null(FALSE) {}
  virtual ~Aggregator_distinct ();
  Aggregator_type Aggrtype() { return DISTINCT_AGGREGATOR; }

  bool setup(THD *);
  void clear(); 
  bool add();
  void endup();
  virtual my_decimal *arg_val_decimal(my_decimal * value);
  virtual double arg_val_real();
  virtual bool arg_is_null();

  bool unique_walk_function(void *element);
  bool unique_walk_function_for_count(void *element);
  static int composite_key_cmp(void* arg, uchar* key1, uchar* key2);
};


/**
  The pass-through aggregator. 
  Implements AGGFN (DISTINCT ..) by knowing it gets distinct data on input. 
  So it just pumps them back to the Item_sum descendant class.
*/
class Aggregator_simple : public Aggregator
{
public:

  Aggregator_simple (Item_sum *sum) :
    Aggregator(sum) {}
  Aggregator_type Aggrtype() { return Aggregator::SIMPLE_AGGREGATOR; }

  bool setup(THD * thd) { return item_sum->setup(thd); }
  void clear() { item_sum->clear(); }
  bool add() { return item_sum->add(); }
  void endup() {};
  virtual my_decimal *arg_val_decimal(my_decimal * value);
  virtual double arg_val_real();
  virtual bool arg_is_null();
};


class Item_sum_num :public Item_sum
{
protected:
  /*
   val_xxx() functions may be called several times during the execution of a 
   query. Derived classes that require extensive calculation in val_xxx()
   maintain cache of aggregate value. This variable governs the validity of 
   that cache.
  */
  bool is_evaluated;
public:
  Item_sum_num() :Item_sum(),is_evaluated(FALSE) {}
  Item_sum_num(Item *item_par) 
    :Item_sum(item_par), is_evaluated(FALSE) {}
  Item_sum_num(Item *a, Item* b) :Item_sum(a,b),is_evaluated(FALSE) {}
  Item_sum_num(List<Item> &list) 
    :Item_sum(list), is_evaluated(FALSE) {}
  Item_sum_num(THD *thd, Item_sum_num *item) 
    :Item_sum(thd, item),is_evaluated(item->is_evaluated) {}
  bool fix_fields(THD *, Item **);
  longlong val_int()
  {
    DBUG_ASSERT(fixed == 1);
    return (longlong) rint(val_real());             /* Real as default */
  }
  String *val_str(String*str);
  my_decimal *val_decimal(my_decimal *);
  void reset_field();
};


class Item_sum_int :public Item_sum_num
{
public:
  Item_sum_int(Item *item_par) :Item_sum_num(item_par) {}
  Item_sum_int(List<Item> &list) :Item_sum_num(list) {}
  Item_sum_int(THD *thd, Item_sum_int *item) :Item_sum_num(thd, item) {}
  double val_real() { DBUG_ASSERT(fixed == 1); return (double) val_int(); }
  String *val_str(String*str);
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return INT_RESULT; }
  void fix_length_and_dec()
  { decimals=0; max_length=21; maybe_null=null_value=0; }
};


class Item_sum_sum :public Item_sum_num
{
protected:
  Item_result hybrid_type;
  double sum;
  my_decimal dec_buffs[2];
  uint curr_dec_buff;
  void fix_length_and_dec();

public:
  Item_sum_sum(Item *item_par, bool distinct) :Item_sum_num(item_par) 
  {
    set_distinct(distinct);
  }
  Item_sum_sum(THD *thd, Item_sum_sum *item);
  enum Sumfunctype sum_func () const 
  { 
    return has_with_distinct() ? SUM_DISTINCT_FUNC : SUM_FUNC; 
  }
  void clear();
  bool add();
  double val_real();
  longlong val_int();
  String *val_str(String*str);
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return hybrid_type; }
  void reset_field();
  void update_field();
  void no_rows_in_result() {}
  const char *func_name() const 
  { 
    return has_with_distinct() ? "sum(distinct " : "sum("; 
  }
  Item *copy_or_same(THD* thd);
};


class Item_sum_count :public Item_sum_int
{
  longlong count;

  friend class Aggregator_distinct;

  void clear();
  bool add();
  void cleanup();

  public:
  Item_sum_count(Item *item_par)
    :Item_sum_int(item_par),count(0)
  {}

  /**
    Constructs an instance for COUNT(DISTINCT)

    @param list  a list of the arguments to the aggregate function

    This constructor is called by the parser only for COUNT (DISTINCT).
  */

  Item_sum_count(List<Item> &list)
    :Item_sum_int(list),count(0)
  {
    set_distinct(TRUE);
  }
  Item_sum_count(THD *thd, Item_sum_count *item)
    :Item_sum_int(thd, item), count(item->count)
  {}
  enum Sumfunctype sum_func () const 
  { 
    return has_with_distinct() ? COUNT_DISTINCT_FUNC : COUNT_FUNC; 
  }
  void no_rows_in_result() { count=0; }
  void make_const(longlong count_arg) 
  { 
    count=count_arg;
    Item_sum::make_const();
  }
  longlong val_int();
  void reset_field();
  void update_field();
  const char *func_name() const 
  { 
    return has_with_distinct() ? "count(distinct " : "count(";
  }
  Item *copy_or_same(THD* thd);
};


/* Item to get the value of a stored sum function */

class Item_sum_avg;

class Item_avg_field :public Item_result_field
{
public:
  Field *field;
  Item_result hybrid_type;
  uint f_precision, f_scale, dec_bin_size;
  uint prec_increment;
  Item_avg_field(Item_result res_type, Item_sum_avg *item);
  enum Type type() const { return FIELD_AVG_ITEM; }
  double val_real();
  longlong val_int();
  my_decimal *val_decimal(my_decimal *);
  bool is_null() { update_null_value(); return null_value; }
  String *val_str(String*);
  enum_field_types field_type() const
  {
    return hybrid_type == DECIMAL_RESULT ?
      MYSQL_TYPE_NEWDECIMAL : MYSQL_TYPE_DOUBLE;
  }
  void fix_length_and_dec() {}
  enum Item_result result_type () const { return hybrid_type; }
  bool check_vcol_func_processor(uchar *int_arg) 
  {
    return trace_unsupported_by_check_vcol_func_processor("avg_field");
  }
  const char *func_name() const { DBUG_ASSERT(0); return "avg_field"; }
};


class Item_sum_avg :public Item_sum_sum
{
public:
  ulonglong count;
  uint prec_increment;
  uint f_precision, f_scale, dec_bin_size;

  Item_sum_avg(Item *item_par, bool distinct) 
    :Item_sum_sum(item_par, distinct), count(0) 
  {}
  Item_sum_avg(THD *thd, Item_sum_avg *item)
    :Item_sum_sum(thd, item), count(item->count),
    prec_increment(item->prec_increment) {}

  void fix_length_and_dec();
  enum Sumfunctype sum_func () const 
  {
    return has_with_distinct() ? AVG_DISTINCT_FUNC : AVG_FUNC;
  }
  void clear();
  bool add();
  double val_real();
  // In SPs we might force the "wrong" type with select into a declare variable
  longlong val_int() { return (longlong) rint(val_real()); }
  my_decimal *val_decimal(my_decimal *);
  String *val_str(String *str);
  void reset_field();
  void update_field();
  Item *result_item(Field *field)
  { return new Item_avg_field(hybrid_type, this); }
  void no_rows_in_result() {}
  const char *func_name() const 
  { 
    return has_with_distinct() ? "avg(distinct " : "avg("; 
  }
  Item *copy_or_same(THD* thd);
  Field *create_tmp_field(bool group, TABLE *table, uint convert_blob_length);
  void cleanup()
  {
    count= 0;
    Item_sum_sum::cleanup();
  }
};

class Item_sum_variance;

class Item_variance_field :public Item_result_field
{
public:
  Field *field;
  Item_result hybrid_type;
  uint f_precision0, f_scale0;
  uint f_precision1, f_scale1;
  uint dec_bin_size0, dec_bin_size1;
  uint sample;
  uint prec_increment;
  Item_variance_field(Item_sum_variance *item);
  enum Type type() const {return FIELD_VARIANCE_ITEM; }
  double val_real();
  longlong val_int()
  { /* can't be fix_fields()ed */ return (longlong) rint(val_real()); }
  String *val_str(String *str)
  { return val_string_from_real(str); }
  my_decimal *val_decimal(my_decimal *dec_buf)
  { return val_decimal_from_real(dec_buf); }
  bool is_null() { update_null_value(); return null_value; }
  enum_field_types field_type() const
  {
    return hybrid_type == DECIMAL_RESULT ?
      MYSQL_TYPE_NEWDECIMAL : MYSQL_TYPE_DOUBLE;
  }
  void fix_length_and_dec() {}
  enum Item_result result_type () const { return hybrid_type; }
  bool check_vcol_func_processor(uchar *int_arg) 
  {
    return trace_unsupported_by_check_vcol_func_processor("var_field");
  }
  const char *func_name() const { DBUG_ASSERT(0); return "variance_field"; }
};


/*
  variance(a) =

  =  sum (ai - avg(a))^2 / count(a) )
  =  sum (ai^2 - 2*ai*avg(a) + avg(a)^2) / count(a)
  =  (sum(ai^2) - sum(2*ai*avg(a)) + sum(avg(a)^2))/count(a) = 
  =  (sum(ai^2) - 2*avg(a)*sum(a) + count(a)*avg(a)^2)/count(a) = 
  =  (sum(ai^2) - 2*sum(a)*sum(a)/count(a) + count(a)*sum(a)^2/count(a)^2 )/count(a) = 
  =  (sum(ai^2) - 2*sum(a)^2/count(a) + sum(a)^2/count(a) )/count(a) = 
  =  (sum(ai^2) - sum(a)^2/count(a))/count(a)

But, this falls prey to catastrophic cancellation.  Instead, use the recurrence formulas

  M_{1} = x_{1}, ~ M_{k} = M_{k-1} + (x_{k} - M_{k-1}) / k newline 
  S_{1} = 0, ~ S_{k} = S_{k-1} + (x_{k} - M_{k-1}) times (x_{k} - M_{k}) newline
  for 2 <= k <= n newline
  ital variance = S_{n} / (n-1)

*/

class Item_sum_variance : public Item_sum_num
{
  void fix_length_and_dec();

public:
  Item_result hybrid_type;
  int cur_dec;
  double recurrence_m, recurrence_s;    /* Used in recurrence relation. */
  ulonglong count;
  uint f_precision0, f_scale0;
  uint f_precision1, f_scale1;
  uint dec_bin_size0, dec_bin_size1;
  uint sample;
  uint prec_increment;

  Item_sum_variance(Item *item_par, uint sample_arg) :Item_sum_num(item_par),
    hybrid_type(REAL_RESULT), count(0), sample(sample_arg)
    {}
  Item_sum_variance(THD *thd, Item_sum_variance *item);
  enum Sumfunctype sum_func () const { return VARIANCE_FUNC; }
  void clear();
  bool add();
  double val_real();
  my_decimal *val_decimal(my_decimal *);
  void reset_field();
  void update_field();
  Item *result_item(Field *field)
  { return new Item_variance_field(this); }
  void no_rows_in_result() {}
  const char *func_name() const
    { return sample ? "var_samp(" : "variance("; }
  Item *copy_or_same(THD* thd);
  Field *create_tmp_field(bool group, TABLE *table, uint convert_blob_length);
  enum Item_result result_type () const { return REAL_RESULT; }
  void cleanup()
  {
    count= 0;
    Item_sum_num::cleanup();
  }
};

class Item_sum_std;

class Item_std_field :public Item_variance_field
{
public:
  Item_std_field(Item_sum_std *item);
  enum Type type() const { return FIELD_STD_ITEM; }
  double val_real();
  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"; }
};

/*
   standard_deviation(a) = sqrt(variance(a))
*/

class Item_sum_std :public Item_sum_variance
{
  public:
  Item_sum_std(Item *item_par, uint sample_arg)
    :Item_sum_variance(item_par, sample_arg) {}
  Item_sum_std(THD *thd, Item_sum_std *item)
    :Item_sum_variance(thd, item)
    {}
  enum Sumfunctype sum_func () const { return STD_FUNC; }
  double val_real();
  Item *result_item(Field *field)
    { return new Item_std_field(this); }
  const char *func_name() const { return "std("; }
  Item *copy_or_same(THD* thd);
  enum Item_result result_type () const { return REAL_RESULT; }
  enum_field_types field_type() const { return MYSQL_TYPE_DOUBLE;}
};

// 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:
  Item_cache *value, *arg_cache;
  Arg_comparator *cmp;
  Item_result hybrid_type;
  enum_field_types hybrid_field_type;
  int cmp_sign;
  bool was_values;  // Set if we have found at least one row (for max/min only)
  bool was_null_value;

  public:
  Item_sum_hybrid(Item *item_par,int sign)
    :Item_sum(item_par), value(0), arg_cache(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(thd, item), value(item->value), arg_cache(0),
    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_hybrid(Item *item, Item *value_arg);
  void clear();
  double val_real();
  longlong val_int();
  my_decimal *val_decimal(my_decimal *);
  void reset_field();
  String *val_str(String *);
  bool keep_field_type(void) const { return 1; }
  enum Item_result result_type () const { return hybrid_type; }
  enum enum_field_types field_type() const { return hybrid_field_type; }
  void update_field();
  void min_max_update_str_field();
  void min_max_update_real_field();
  void min_max_update_int_field();
  void min_max_update_decimal_field();
  void cleanup();
  bool any_value() { return was_values; }
  void no_rows_in_result();
  void restore_to_before_no_rows_in_result();
  Field *create_tmp_field(bool group, TABLE *table,
			  uint convert_blob_length);
};


class Item_sum_min :public Item_sum_hybrid
{
public:
  Item_sum_min(Item *item_par) :Item_sum_hybrid(item_par,1) {}
  Item_sum_min(THD *thd, Item_sum_min *item) :Item_sum_hybrid(thd, item) {}
  enum Sumfunctype sum_func () const {return MIN_FUNC;}

  bool add();
  const char *func_name() const { return "min("; }
  Item *copy_or_same(THD* thd);
};


class Item_sum_max :public Item_sum_hybrid
{
public:
  Item_sum_max(Item *item_par) :Item_sum_hybrid(item_par,-1) {}
  Item_sum_max(THD *thd, Item_sum_max *item) :Item_sum_hybrid(thd, item) {}
  enum Sumfunctype sum_func () const {return MAX_FUNC;}

  bool add();
  const char *func_name() const { return "max("; }
  Item *copy_or_same(THD* thd);
};


class Item_sum_bit :public Item_sum_int
{
protected:
  ulonglong reset_bits,bits;

public:
  Item_sum_bit(Item *item_par,ulonglong reset_arg)
    :Item_sum_int(item_par),reset_bits(reset_arg),bits(reset_arg) {}
  Item_sum_bit(THD *thd, Item_sum_bit *item):
    Item_sum_int(thd, item), reset_bits(item->reset_bits), bits(item->bits) {}
  enum Sumfunctype sum_func () const {return SUM_BIT_FUNC;}
  void clear();
  longlong val_int();
  void reset_field();
  void update_field();
  void fix_length_and_dec()
  { decimals= 0; max_length=21; unsigned_flag= 1; maybe_null= null_value= 0; }
  void cleanup()
  {
    bits= reset_bits;
    Item_sum_int::cleanup();
  }
};


class Item_sum_or :public Item_sum_bit
{
public:
  Item_sum_or(Item *item_par) :Item_sum_bit(item_par, 0) {}
  Item_sum_or(THD *thd, Item_sum_or *item) :Item_sum_bit(thd, item) {}
  bool add();
  const char *func_name() const { return "bit_or("; }
  Item *copy_or_same(THD* thd);
};


class Item_sum_and :public Item_sum_bit
{
  public:
  Item_sum_and(Item *item_par) :Item_sum_bit(item_par, ULONGLONG_MAX) {}
  Item_sum_and(THD *thd, Item_sum_and *item) :Item_sum_bit(thd, item) {}
  bool add();
  const char *func_name() const { return "bit_and("; }
  Item *copy_or_same(THD* thd);
};

class Item_sum_xor :public Item_sum_bit
{
  public:
  Item_sum_xor(Item *item_par) :Item_sum_bit(item_par, 0) {}
  Item_sum_xor(THD *thd, Item_sum_xor *item) :Item_sum_bit(thd, item) {}
  bool add();
  const char *func_name() const { return "bit_xor("; }
  Item *copy_or_same(THD* thd);
};


/*
  User defined aggregates
*/

#ifdef HAVE_DLOPEN

class Item_udf_sum : public Item_sum
{
protected:
  udf_handler udf;

public:
  Item_udf_sum(udf_func *udf_arg)
    :Item_sum(), udf(udf_arg)
  { quick_group=0; }
  Item_udf_sum(udf_func *udf_arg, List<Item> &list)
    :Item_sum(list), udf(udf_arg)
  { quick_group=0;}
  Item_udf_sum(THD *thd, Item_udf_sum *item)
    :Item_sum(thd, item), udf(item->udf)
  { udf.not_original= TRUE; }
  const char *func_name() const { return udf.name(); }
  bool fix_fields(THD *thd, Item **ref)
  {
    DBUG_ASSERT(fixed == 0);

    if (init_sum_func_check(thd))
      return TRUE;

    fixed= 1;
    if (udf.fix_fields(thd, this, this->arg_count, this->args))
      return TRUE;

    memcpy (orig_args, args, sizeof (Item *) * arg_count);
    return check_sum_func(thd, ref);
  }
  enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }
  virtual bool have_field_update(void) const { return 0; }

  void clear();
  bool add();
  void reset_field() {};
  void update_field() {};
  void cleanup();
  virtual void print(String *str, enum_query_type query_type);
};


class Item_sum_udf_float :public Item_udf_sum
{
 public:
  Item_sum_udf_float(udf_func *udf_arg)
    :Item_udf_sum(udf_arg) {}
  Item_sum_udf_float(udf_func *udf_arg, List<Item> &list)
    :Item_udf_sum(udf_arg, list) {}
  Item_sum_udf_float(THD *thd, Item_sum_udf_float *item)
    :Item_udf_sum(thd, item) {}
  longlong val_int()
  {
    DBUG_ASSERT(fixed == 1);
    return (longlong) rint(Item_sum_udf_float::val_real());
  }
  double val_real();
  String *val_str(String*str);
  my_decimal *val_decimal(my_decimal *);
  void fix_length_and_dec() { fix_num_length_and_dec(); }
  Item *copy_or_same(THD* thd);
};


class Item_sum_udf_int :public Item_udf_sum
{
public:
  Item_sum_udf_int(udf_func *udf_arg)
    :Item_udf_sum(udf_arg) {}
  Item_sum_udf_int(udf_func *udf_arg, List<Item> &list)
    :Item_udf_sum(udf_arg, list) {}
  Item_sum_udf_int(THD *thd, Item_sum_udf_int *item)
    :Item_udf_sum(thd, item) {}
  longlong val_int();
  double val_real()
    { DBUG_ASSERT(fixed == 1); return (double) Item_sum_udf_int::val_int(); }
  String *val_str(String*str);
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return INT_RESULT; }
  void fix_length_and_dec() { decimals=0; max_length=21; }
  Item *copy_or_same(THD* thd);
};


class Item_sum_udf_str :public Item_udf_sum
{
public:
  Item_sum_udf_str(udf_func *udf_arg)
    :Item_udf_sum(udf_arg) {}
  Item_sum_udf_str(udf_func *udf_arg, List<Item> &list)
    :Item_udf_sum(udf_arg,list) {}
  Item_sum_udf_str(THD *thd, Item_sum_udf_str *item)
    :Item_udf_sum(thd, item) {}
  String *val_str(String *);
  double val_real()
  {
    int err_not_used;
    char *end_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;
  }
  longlong val_int()
  {
    int err_not_used;
    char *end;
    String *res;
    CHARSET_INFO *cs;

    if (!(res= val_str(&str_value)))
      return 0;                                 /* Null value */
    cs= res->charset();
    end= (char*) res->ptr()+res->length();
    return cs->cset->strtoll10(cs, res->ptr(), &end, &err_not_used);
  }
  my_decimal *val_decimal(my_decimal *dec);
  enum Item_result result_type () const { return STRING_RESULT; }
  void fix_length_and_dec();
  Item *copy_or_same(THD* thd);
};


class Item_sum_udf_decimal :public Item_udf_sum
{
public:
  Item_sum_udf_decimal(udf_func *udf_arg)
    :Item_udf_sum(udf_arg) {}
  Item_sum_udf_decimal(udf_func *udf_arg, List<Item> &list)
    :Item_udf_sum(udf_arg, list) {}
  Item_sum_udf_decimal(THD *thd, Item_sum_udf_decimal *item)
    :Item_udf_sum(thd, item) {}
  String *val_str(String *);
  double val_real();
  longlong val_int();
  my_decimal *val_decimal(my_decimal *);
  enum Item_result result_type () const { return DECIMAL_RESULT; }
  void fix_length_and_dec() { fix_num_length_and_dec(); }
  Item *copy_or_same(THD* thd);
};

#else /* Dummy functions to get sql_yacc.cc compiled */

class Item_sum_udf_float :public Item_sum_num
{
 public:
  Item_sum_udf_float(udf_func *udf_arg)
    :Item_sum_num() {}
  Item_sum_udf_float(udf_func *udf_arg, List<Item> &list) :Item_sum_num() {}
  Item_sum_udf_float(THD *thd, Item_sum_udf_float *item)
    :Item_sum_num(thd, item) {}
  enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }
  double val_real() { DBUG_ASSERT(fixed == 1); return 0.0; }
  void clear() {}
  bool add() { return 0; }  
  void update_field() {}
};


class Item_sum_udf_int :public Item_sum_num
{
public:
  Item_sum_udf_int(udf_func *udf_arg)
    :Item_sum_num() {}
  Item_sum_udf_int(udf_func *udf_arg, List<Item> &list) :Item_sum_num() {}
  Item_sum_udf_int(THD *thd, Item_sum_udf_int *item)
    :Item_sum_num(thd, item) {}
  enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }
  longlong val_int() { DBUG_ASSERT(fixed == 1); return 0; }
  double val_real() { DBUG_ASSERT(fixed == 1); return 0; }
  void clear() {}
  bool add() { return 0; }  
  void update_field() {}
};


class Item_sum_udf_decimal :public Item_sum_num
{
 public:
  Item_sum_udf_decimal(udf_func *udf_arg)
    :Item_sum_num() {}
  Item_sum_udf_decimal(udf_func *udf_arg, List<Item> &list)
    :Item_sum_num() {}
  Item_sum_udf_decimal(THD *thd, Item_sum_udf_float *item)
    :Item_sum_num(thd, item) {}
  enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }
  double val_real() { DBUG_ASSERT(fixed == 1); return 0.0; }
  my_decimal *val_decimal(my_decimal *) { DBUG_ASSERT(fixed == 1); return 0; }
  void clear() {}
  bool add() { return 0; }
  void update_field() {}
};


class Item_sum_udf_str :public Item_sum_num
{
public:
  Item_sum_udf_str(udf_func *udf_arg)
    :Item_sum_num() {}
  Item_sum_udf_str(udf_func *udf_arg, List<Item> &list)
    :Item_sum_num() {}
  Item_sum_udf_str(THD *thd, Item_sum_udf_str *item)
    :Item_sum_num(thd, item) {}
  String *val_str(String *)
    { DBUG_ASSERT(fixed == 1); null_value=1; return 0; }
  double val_real() { DBUG_ASSERT(fixed == 1); null_value=1; return 0.0; }
  longlong val_int() { DBUG_ASSERT(fixed == 1); null_value=1; return 0; }
  enum Item_result result_type () const { return STRING_RESULT; }
  void fix_length_and_dec() { maybe_null=1; max_length=0; }
  enum Sumfunctype sum_func () const { return UDF_SUM_FUNC; }
  void clear() {}
  bool add() { return 0; }  
  void update_field() {}
};

#endif /* HAVE_DLOPEN */

C_MODE_START
int group_concat_key_cmp_with_distinct(void* arg, const void* key1,
                                       const void* key2);
int group_concat_key_cmp_with_order(void* arg, const void* key1,
                                    const void* key2);
int dump_leaf_key(void* key_arg,
                  element_count count __attribute__((unused)),
                  void* item_arg);
C_MODE_END

class Item_func_group_concat : public Item_sum
{
  TMP_TABLE_PARAM *tmp_table_param;
  String result;
  String *separator;
  TREE tree_base;
  TREE *tree;

  /**
     If DISTINCT is used with this GROUP_CONCAT, this member is used to filter
     out duplicates. 
     @see Item_func_group_concat::setup
     @see Item_func_group_concat::add
     @see Item_func_group_concat::clear
   */
  Unique *unique_filter;
  TABLE *table;
  ORDER **order;
  Name_resolution_context *context;
  /** The number of ORDER BY items. */
  uint arg_count_order;
  /** The number of selected items, aka the expr list. */
  uint arg_count_field;
  uint row_count;
  bool distinct;
  bool warning_for_row;
  bool always_null;
  bool force_copy_fields;
  bool no_appended;
  /*
    Following is 0 normal object and pointer to original one for copy
    (to correctly free resources)
  */
  Item_func_group_concat *original;

  friend int group_concat_key_cmp_with_distinct(void* arg, const void* key1,
                                                const void* key2);
  friend int group_concat_key_cmp_with_order(void* arg, const void* key1,
					     const void* key2);
  friend int dump_leaf_key(void* key_arg,
                           element_count count __attribute__((unused)),
			   void* item_arg);

public:
  Item_func_group_concat(Name_resolution_context *context_arg,
                         bool is_distinct, List<Item> *is_select,
                         SQL_I_List<ORDER> *is_order, String *is_separator);

  Item_func_group_concat(THD *thd, Item_func_group_concat *item);
  ~Item_func_group_concat();
  void cleanup();

  enum Sumfunctype sum_func () const {return GROUP_CONCAT_FUNC;}
  const char *func_name() const { return "group_concat"; }
  virtual Item_result result_type () const { return STRING_RESULT; }
  virtual Field *make_string_field(TABLE *table);
  enum_field_types field_type() const
  {
    if (too_big_for_varchar())
      return MYSQL_TYPE_BLOB;
    else
      return MYSQL_TYPE_VARCHAR;
  }
  void clear();
  bool add();
  void reset_field() { DBUG_ASSERT(0); }        // not used
  void update_field() { DBUG_ASSERT(0); }       // not used
  bool fix_fields(THD *,Item **);
  bool setup(THD *thd);
  void make_unique();
  double val_real()
  {
    int error;
    const char *end;
    String *res;
    if (!(res= val_str(&str_value)))
      return 0.0;
    end= res->ptr() + res->length();
    return (my_strtod(res->ptr(), (char**) &end, &error));
  }
  longlong val_int()
  {
    String *res;
    char *end_ptr;
    int error;
    if (!(res= val_str(&str_value)))
      return (longlong) 0;
    end_ptr= (char*) res->ptr()+ res->length();
    return my_strtoll10(res->ptr(), &end_ptr, &error);
  }
  my_decimal *val_decimal(my_decimal *decimal_value)
  {
    return val_decimal_from_string(decimal_value);
  }
  String* val_str(String* str);
  Item *copy_or_same(THD* thd);
  void no_rows_in_result() {}
  virtual void print(String *str, enum_query_type query_type);
  virtual bool change_context_processor(uchar *cntx)
    { context= (Name_resolution_context *)cntx; return FALSE; }
};

#endif /* ITEM_SUM_INCLUDED */