These methods:

Item_date_add_interval::get_date()

Item_func_add_time::get_date()

have tests for field_type(). This is not friendly to new data types, which might want to have these functions in addition to the currently supported data types DATETIME, DATE, TIME.

Near future candidates:

• TIMESTAMP: Soon we'll change the temporal arithmetic to preserve the MYSQL_TYPE_TIMESTAMP type (MDEV-15750).
• TIMESTAMP WITH TIME ZONE

Also, we'll introduce INTERVAL data types natively and it will be possible to use intervals outside of the temporal arithmetic context, e.g.:

CREATE TABLE t1 (a INTERVAL HOUR TO SECOND);

INSERT INTO t1 VALUES (INTERVAL '10:20:30' HOUR TO SECOND);

SELECT * FROM t1 WHERE COALESCE(a, INTERVAL '00:00:00' HOUR TO SECOND) = INTERVAL '10:00:00' HOUR TO SECOND;

So, these syntax tricks:

        | bit_expr '+' INTERVAL_SYM expr interval %prec '+'

          {

            $$= new (thd->mem_root) Item_date_add_interval(thd, $1, $4, $5, 0);

            if (unlikely($$ == NULL))

              MYSQL_YYABORT;

          }

        | DATE_ADD_INTERVAL '(' expr ',' INTERVAL_SYM expr interval ')'

          {

            $$= new (thd->mem_root) Item_date_add_interval(thd, $3, $6, $7, 0);

            if (unlikely($$ == NULL))

              MYSQL_YYABORT;

          }

will disappear soon. The syntax for interval expressions will migrate to the rule simple_expr. Expressions starting with the INTERVAL keyword will become normal expressions with they own Type_handler.

To make it possible for new data types to add their own implementations for ADDTIME()/SUBTIME(), DATE_ADD(), DATE_SUB(), as well as for the operators + and -, we'll do the following:

• Introduce a new class Item_handled_func, with approximately this prototype:

  class Item_handled_func: public Item_func

  {

  public:

  class Handler

  {

  public:

  virtual ~Handler() { }

  virtual String *val_str(Item_handled_func *, String *) const= 0;

  virtual String *val_str_ascii(Item_handled_func *, String *) const= 0;

  virtual double val_real(Item_handled_func *) const= 0;

  virtual longlong val_int(Item_handled_func *) const= 0;

  virtual my_decimal *val_decimal(Item_handled_func *, my_decimal *) const= 0;

  virtual bool get_date(Item_handled_func *, MYSQL_TIME *, ulonglong fuzzydate) const= 0;

  virtual const Type_handler *return_type_handler() const= 0;

  virtual bool fix_length_and_dec(Item_handled_func *) const= 0;

  };

  protected:

  const Handler *m_func_handler;

  public:

  Item_handled_func(THD *thd, Item *a)

  :Item_func(thd, a), m_func_handler(NULL) { }

  Item_handled_func(THD *thd, Item *a, Item *b)

  :Item_func(thd, a, b), m_func_handler(NULL) { }

  void set_func_handler(const Handler *handler)

  {

  m_func_handler= handler;

  }

  const Type_handler *type_handler() const

  {

  return m_func_handler->return_type_handler();

  }

  String *val_str(String *to)

  {

  return m_func_handler->val_str(this, to);

  }

  String *val_str_ascii(String *to)

  {

  return m_func_handler->val_str_ascii(this, to);

  }

  double val_real()

  {

  return m_func_handler->val_real(this);

  }

  longlong val_int()

  {

  return m_func_handler->val_int(this);

  }

  my_decimal *val_decimal(my_decimal *to)

  {

  return m_func_handler->val_decimal(this, to);

  }

  bool get_date(MYSQL_TIME *to, ulonglong fuzzydate)

  {

  return m_func_handler->get_date(this, to, fuzzydate);

  }

  };

• Change Item_func_add_time, Item_date_add_interval, Item_func_str_to_date to derive from the new class Item_handled_func.
• Remove class Item_temporal_hybrid_func
• Add handler classes for the former Item_temporal_hybrid_func descendants:

  Item_handled_func::Handler

  Func_handler_temporal_hybrid

  Func_handler_date_add_interval

  Func_handler_date_add_interval_datetime

  Func_handler_date_add_interval_date

  Func_handler_date_add_interval_time

  Func_handler_date_add_interval_string

  Func_handler_add_time

  Func_handler_add_time_datetime

  Func_handler_add_time_time

  Func_handler_add_time_string

  Func_handler_str_to_date_datetime

  Func_handler_str_to_date_datetime_sec

  Func_handler_str_to_date_datetime_usec

  Func_handler_str_to_date_date

  Func_handler_str_to_date_time

  Func_handler_str_to_date_time_sec

  Func_handler_str_to_date_time_usec

• Move the code from Item_func_xxx::get_date() and Item_func_xxx::fix_length_and_dec() to the corresponding methods in Func_handler_xxx

After this change:

• All tests for field_type() inside Item_func_xxx::get_date() will be gone
• The block in Item_func_xxx::fix_length_and_dec() which decides the data type and its attributes will be simplified. For example:

  bool Item_date_add_interval::fix_length_and_dec()

  {

  ..

  arg0_field_type= args[0]->field_type();

  if (arg0_field_type == MYSQL_TYPE_DATETIME ||

  arg0_field_type == MYSQL_TYPE_TIMESTAMP)

  {

  set_func_handler(&func_handler_date_add_interval_datetime);

  }

  else if (arg0_field_type == MYSQL_TYPE_DATE)

  {

  if (int_type <= INTERVAL_DAY || int_type == INTERVAL_YEAR_MONTH)

  set_func_handler(&func_handler_date_add_interval_date);

  else

  set_func_handler(&func_handler_date_add_interval_datetime);

  }

  else if (arg0_field_type == MYSQL_TYPE_TIME)

  {

  if (int_type >= INTERVAL_DAY && int_type != INTERVAL_YEAR_MONTH)

  set_func_handler(&func_handler_date_add_interval_time);

  else

  set_func_handler(&func_handler_date_add_interval_datetime_arg0_time);

  }

  else

  {

  set_func_handler(&func_handler_date_add_interval_string);

  }

  maybe_null= true;

  return m_func_handler->fix_length_and_dec(this);

  }

  Notice, the above code does not set attributes directly anymore. Attributes are set by the call for m_func_handler->fix_length_and_dec(this).

Note, after this change, the fix_length_and_dec() part will sill have conditions testing field_type(). This is OK. This main goal of this task is to remove field_type() tests from get_date()! The remaining tests in fix_length_and_dec() will be removed in a separate change, when we add a registry of overloaded functions (in a way similar to how we added Type_aggregator for comparison functions and for CASE and its abbreviations).

Note, this task does not touch Item_func_plus and Item_func_minus. Eventually they'll also be changed to derive from Item_handled_func, in a separate task.