SELECT day_price.date, day_price.price,
CASE
    WHEN default_price.price = day_price.price
    THEN 'цена по-умолчанию'
    ELSE 'особая цена'
    END as price_type
FROM day_price
JOIN default_price ON day_price.id = default_price.id
WHERE default_price.id = 53 AND day_price.date BETWEEN '2014-10-01' AND '2014-10-20'
ORDER by date ASC

DROP PROCEDURE IF EXISTS create_temp_table;
DELIMITER //
CREATE PROCEDURE create_temp_table(
        IN begin_date DATE,
        IN end_date DATE
    )
    DETERMINISTIC    
BEGIN
    
    SET @last_date = begin_date;
    
    DROP TABLE IF EXISTS temp_calendar;
    
    CREATE TEMPORARY TABLE temp_calendar(
           date DATE NOT NULL,
           KEY days (date)
    ) ENGINE = MyIsam;
    
    WHILE @last_date <= end_date DO
       insert into temp_calendar(date) values(@last_date);
       SET @last_date = DATE_ADD(@last_date, interval 1 day);
    END WHILE;
  
END //

SELECT create_temp_table('2014-10-01','2014-10-20'), day_price.date, day_price.price,
CASE
    WHEN default_price.price = day_price.price
    THEN 'цена по-умолчанию'
    ELSE 'особая цена'
    END as price_type
FROM day_price
JOIN default_price ON day_price.id = default_price.id
LEFT JOIN temp_calendar ON temp_calendar.date = day_price.date
WHERE default_price.id = 53 AND day_price.date BETWEEN '2014-10-01' AND '2014-10-20'
ORDER by date ASC

DROP PROCEDURE IF EXISTS create_temp_table;
DELIMITER //
CREATE PROCEDURE create_temp_table(
        IN begin_date DATE,
        IN end_date DATE
    )
    DETERMINISTIC    
BEGIN    
    SET @last_date = begin_date;    
    DROP TABLE IF EXISTS temp_calendar;    
    CREATE TEMPORARY TABLE temp_calendar(
           date DATE NOT NULL,
           KEY days (date)
    ) ENGINE = innoDB;    
    WHILE @last_date <= end_date DO
       insert into temp_calendar(date) values(@last_date);
       SET @last_date = DATE_ADD(@last_date, interval 1 day);
    END WHILE;  
END //
CALL create_temp_table('2014-10-01','2014-10-20');
SELECT temp_calendar.date, 
IF(day_price.price is null, 'цена по-умолчанию', 'особая цена') as price_type, 
IF (day_price.price is null,(SELECT default_price.price from default_price WHERE default_price.id=53), day_price.price) as price       
FROM temp_calendar LEFT JOIN day_price 
ON (temp_calendar.`date` = day_price.`date` AND day_price.id = 53
AND day_price.date BETWEEN '2014-10-01' AND '2014-10-20'), default_price 
WHERE default_price.id = 53
ORDER by temp_calendar.date ASC;