mysql fill in missing dates

MySQL doesn't have recursive functionality, so you're left with using the NUMBERS table trick -

Create a table that only holds incrementing numbers - easy to do using an auto_increment:

DROP TABLE IF EXISTS `example`.`numbers`;
CREATE TABLE  `example`.`numbers` (
  `id` int(10) unsigned NOT NULL auto_increment,
   PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Populate the table using:

INSERT INTO `example`.`numbers`
  ( `id` )
VALUES
  ( NULL )
...for as many values as you need.

Use DATE_ADD to construct a list of dates, increasing the days based on the NUMBERS.id value. Replace "2010-06-06" and "2010-06-14" with your respective start and end dates (but use the same format, YYYY-MM-DD) -

SELECT `x`.*
  FROM (SELECT DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY)
          FROM `numbers` `n`
         WHERE DATE_ADD('2010-06-06', INTERVAL `n`.`id` -1 DAY) <= '2010-06-14' ) x
LEFT JOIN onto your table of data based on the time portion:

   SELECT `x`.`ts` AS `timestamp`,
          COALESCE(`y`.`score`, 0) AS `cnt`
     FROM (SELECT DATE_FORMAT(DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY), '%m/%d/%Y') AS `ts`
             FROM `numbers` `n`
            WHERE DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY) <= '2010-06-14') x
LEFT JOIN TABLE `y` ON STR_TO_DATE(`y`.`date`, '%d.%m.%Y') = `x`.`ts`
If you want to maintain the date format, use the DATE_FORMAT function:

DATE_FORMAT(`x`.`ts`, '%d.%m.%Y') AS `timestamp`