Add Type_handler::decimal_precision()

uint Item::decimal_precision() const

{

  Item_result restype= result_type();

  if ((restype == DECIMAL_RESULT) || (restype == INT_RESULT))

  {

    uint prec= 

      my_decimal_length_to_precision(max_char_length(), decimals,

                                     unsigned_flag);

    return MY_MIN(prec, DECIMAL_MAX_PRECISION);

  }

  uint res= max_char_length();

  /*

    Return at least one decimal digit, even if Item::max_char_length()

    returned  0. This is important to avoid attempts to create fields of types

    INT(0) or DECIMAL(0,0) when converting NULL or empty strings to INT/DECIMAL:

      CREATE TABLE t1 AS SELECT CONVERT(NULL,SIGNED) AS a;

  */

  return res ? MY_MIN(res, DECIMAL_MAX_PRECISION) : 1;

}

virtual uint Item_decimal_precision(const Item *item) const;