帮我写一个SQL Crosstab查询

Question

我有3个表看起来像这样:

tblVideo:
    VideoID     |   Video Name
          1             video 1
          2             video 2
          3             video 3
          4             video 4

tblCategory:
    CategoryID  |   CategoryName
          1           category1
          2           category2
          3           category3

tblVideoCategory:
     VideoID    |    CategoryID
          1               3
          2               1
          2               2
          3               1
          3               2
          3               3
          4               1

我想编写一个返回一个如下所示的表的查询:

vVideoCategory:
VideoID   |   VideoName   |   category1   |   category2   |   category3
   1           video 1           false           false          true 
   2           video 2           true            true           false
   3           video 3           true            true           true
   4           video 4           true            false          false

我试过四处寻找例子,但还没有找到任何看似相同的东西.任何帮助将不胜感激,谢谢.

绝对寻找允许更改和添加/删除类别的内容.

Answer 1

使用：

  SELECT v.videoid,
         v.video_name,
         COALESCE(MAX(CASE WHEN vc.categoryid = 1 THEN 'true' END), 'false') AS category1,
         COALESCE(MAX(CASE WHEN vc.categoryid = 2 THEN 'true' END), 'false') AS category2,
         COALESCE(MAX(CASE WHEN vc.categoryid = 3 THEN 'true' END), 'false') AS category3
    FROM tblvideo v
    JOIN tblvideocategory vc ON vc.videoid = v.videoid
GROUP BY v.videoid, v.video_name

SQL Server 2005+：

DECLARE @SQL AS NVARCHAR(4000)
DECLARE @categoryid AS INT

DECLARE CUR CURSOR FAST_FORWARD FOR
   SELECT c.categoryid
     FROM tblcategory c
 ORDER BY c.categoryid

SET @SQL = N'SELECT v.videoid,
                    v.video_name, '

OPEN CUR
FETCH NEXT FROM CUR INTO @categoryid
WHILE @@FETCH_STATUS = 0
BEGIN

  SET @SQL = @SQL + ' COALESCE(MAX(CASE WHEN vc.categoryid = '+ @categoryid +' THEN 'true' END), 'false') AS category'+ @categoryid +' ,'

  FETCH NEXT FROM CUR INTO @categoryid
END

CLOSE CUR;
DEALLOCATE CUR;

--Get rid of trailing comma at the end
SELECT @SQL = SUBSTRING(@SQL, 1, LEN(@SQL) -1)

SET @SQL = @SQL + ' FROM tblvideo v
                    JOIN tblvideocategory vc ON vc.videoid = v.videoid
                GROUP BY v.videoid, v.video_name 
                ORDER BY v.videoid, v.video_name '

BEGIN

  EXEC sp_executesql @SQL

END