Looking for MySQL help joining two tables based on variable

Question

I know this is a little complicated and I could accomplish this using other methods, but please bear with me.

I am trying to join a table filled with dates with a table filled with events so I can show dates which have no events. I wrote a QUERY that handles this fine, but if I have more than one event on a particular date I can't seem to join multiple records. I have tried all variations of joins.

Please see my problem here

SQL Code

SELECT @RowNumber := @RowNumber + 1 AS DayNumber, D.Date, L.LessonID, L.Title 
FROM dates D 
JOIN (SELECT @RowNumber:= 0) R 
LEFT JOIN lessons L ON L.DayNumber = (@RowNumber+1) 
WHERE D.Date IN ('2012-01-01','2012-01-03','2012-01-05','2012-01-10') 
ORDER BY DayNumber ASC LIMIT 0, 50

Table Schema

CREATE TABLE IF NOT EXISTS `dates` (
  `DateID` int(11) NOT NULL AUTO_INCREMENT,
  `Date` date NOT NULL,
  `TimeStamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`DateID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1;

INSERT INTO `dates` (`DateID`, `Date`, `TimeStamp`) VALUES
(1, '2012-01-01', '2013-02-16 17:38:07'),
(2, '2012-01-02', '2013-02-16 17:38:07'),
(3, '2012-01-03', '2013-02-16 17:38:07'),
(4, '2012-01-04', '2013-02-16 17:38:07'),
(5, '2012-01-05', '2013-02-16 17:38:07'),
(6, '2012-01-06', '2013-02-16 17:38:07'),
(7, '2012-01-07', '2013-02-16 17:38:07'),
(8, '2012-01-08', '2013-02-16 17:38:07'),
(9, '2012-01-09', '2013-02-16 17:38:07'),
(10, '2012-01-10', '2013-02-16 17:38:07');

CREATE TABLE IF NOT EXISTS `lessons` (
  `LessonID` int(11) NOT NULL AUTO_INCREMENT,
  `DayNumber` int(11) NOT NULL DEFAULT '0',
  `Title` varchar(1024) NOT NULL,
  `TimeStamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`LessonID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1;

INSERT INTO `lessons` (`LessonID`, `DayNumber`, `Title`, `TimeStamp`) VALUES
(1, 1, 'asdfasdf', '2012-01-01 18:03:21'),
(2, 1, 'qwerqwer', '2012-01-05 18:03:21'),
(3, 3, '12341234', '2012-01-05 18:03:34');

Results

Right now this returns this:

DAYNUMBER DATE  LESSONID    TITLE
1   January, 01 2012 00:00:00+0000  1   asdfasdf
2   January, 03 2012 00:00:00+0000  (null)  (null)
3   January, 05 2012 00:00:00+0000  3   12341234
4   January, 10 2012 00:00:00+0000  (null)  (null)

But I would like it to return this (note the second row on DayNumber 1 with the title "qwerqwer"):

DAYNUMBER   DATE    LESSONID    TITLE
1   January, 01 2012 00:00:00+0000  1   asdfasdf
1   January, 01 2012 00:00:00+0000  1   qwerqwer
2   January, 03 2012 00:00:00+0000  (null)  (null)
3   January, 05 2012 00:00:00+0000  3   12341234
4   January, 10 2012 00:00:00+0000  (null)  (null)

Answer 1

If I'm understanding your question correctly, you could do something like this:

SELECT T.DayNumber,
  T.Date,
  L.LessonId,
  L.Title
FROM (
  SELECT @RowNumber := @RowNumber + 1 AS DayNumber, 
    D.Date
  FROM dates D 
     JOIN (SELECT @RowNumber:= 0) R 
  WHERE D.Date IN ('2012-01-01','2012-01-03','2012-01-05','2012-01-10') 
) T LEFT JOIN Lessons L ON 
    T.DayNumber = L.DayNumber 
ORDER BY T.DayNumber ASC LIMIT 0, 50

Here is the updated Fiddle .

And here are the results:

DAYNUMBER   DATE                                LESSONID     TITLE
1           January, 01 2012 00:00:00+0000      1            asdfasdf
1           January, 01 2012 00:00:00+0000      2            qwerqwer
2           January, 03 2012 00:00:00+0000      (null)       (null)
3           January, 05 2012 00:00:00+0000      3            12341234
4           January, 10 2012 00:00:00+0000      (null)       (null)

BTW -- In your results above, you have Lesson Id 1 for your 2nd result -- I assume you meant Lesson Id 2 as in the above results.