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我知道这有点复杂，我可以使用其他方法来完成，但请多多包涵。

我正在尝试将一个充满日期的表格与一个充满事件的表格连接起来，这样我就可以显示没有事件的日期。我写了一个可以很好地处理这个问题的查询，但是如果我在特定日期有多个事件，我似乎无法加入多个记录。我已经尝试了所有的连接变体。

请在这里查看我的问题

SQL 代码

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

表架构

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');

结果

现在这会返回：

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)

但我希望它返回这个（注意第 1 天的第二行，标题为“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)
4

1 回答 1

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如果我正确理解您的问题，您可以执行以下操作：

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

这是更新的Fiddle。

结果如下：

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)

顺便说一句——在你上面的结果中，你的第二个结果有第 1 课——我假设你的意思是上面的结果中的第 2 课。

于 2013-02-17T16:21:02.340 回答