添加连接时SQL行消失

SELECT  tblArtworkTemplates.ID, tblArtworkTemplates.dateCreated, tblSpecifications.TxtPagination, tblSpecifications.FlatSizeW AS width, 
         tblSpecifications.FlatSizeL AS length, tblSpecifications.FlatSizeUOM AS uom, 
          (SELECT  COUNT(1) AS Expr1 
          FROM   tblArtworkUploads 
          WHERE  (templateID = tblArtworkTemplates.ID)) AS uploadCount, 
          (SELECT  COUNT(1) AS talks 
          FROM   tblArtworkTemplateMessages 
          WHERE  (templateID = tblArtworkTemplates.ID)) AS talkCount, tblArtworkTemplates.lastEditPing, tblUsers.userName AS Expr1 
FROM   tblUsers INNER JOIN 
         tblArtworkTemplates INNER JOIN 
         tblSpecifications ON tblArtworkTemplates.specID = tblSpecifications.id ON tblUsers.id = tblArtworkTemplates.editPingUserID 
WHERE  (tblArtworkTemplates.userID = 70)

当tblArtworkTemplates.editPingUserID为空时，tblusers连接正在导致行消失。我是否使用错误的连接类型？添加连接时SQL行消失

来源

2011-02-23 Tom Gullen

也许尝试左外连接..或右外连接..

Wikipedia的信息有关加入

来源

2011-02-23 10:40:27 bAN

谢谢，右外连接的作品。这些东西总是让我困惑。 – 2011-02-23 10:41:29

试试这个，您的加入是错误的。

SELECT  tblArtworkTemplates.ID, tblArtworkTemplates.dateCreated, tblSpecifications.TxtPagination, tblSpecifications.FlatSizeW AS width, 
         tblSpecifications.FlatSizeL AS length, tblSpecifications.FlatSizeUOM AS uom, 
          (SELECT  COUNT(1) AS Expr1 
          FROM   tblArtworkUploads 
          WHERE  (templateID = tblArtworkTemplates.ID)) AS uploadCount, 
          (SELECT  COUNT(1) AS talks 
          FROM   tblArtworkTemplateMessages 
          WHERE  (templateID = tblArtworkTemplates.ID)) AS talkCount, tblArtworkTemplates.lastEditPing, tblUsers.userName AS Expr1 
FROM tblUsers u 
    INNER JOIN tblArtworkTemplates a ON u.id = a.editPingUserID 
    INNER JOIN tblSpecifications s ON a.specID = s.id ON 
WHERE  (a.userID = 70)

来源

2011-02-23 10:42:19 Ryk

如果在双连接之后引用double-on子句，则连接并非“错误”。它的工作原理和有效的语法 – RichardTheKiwi 2011-02-23 10:44:10

这取决于你在做什么。

如果您总是需要来自tblUsers的记录，但是仅当数据来自（换句话说，如果模板没有规范，您不关心模板）的Template + Specification中的数据，，使用此

FROM tblUsers 
LEFT JOIN 
     tblArtworkTemplates 
     INNER JOIN tblSpecifications 
      ON tblArtworkTemplates.specID = tblSpecifications.id 
    ON tblUsers.id = tblArtworkTemplates.editPingUserID

如果你总是想从向tblUsers记录，但数据从模板（如果有），然后从规格如有（换句话说，如果模板是可用的无说明书，获取数据从模板记录反正），然后用这个

FROM tblUsers 
LEFT JOIN 
     tblArtworkTemplates 
     LEFT JOIN tblSpecifications 
      ON tblArtworkTemplates.specID = tblSpecifications.id 
    ON tblUsers.id = tblArtworkTemplates.editPingUserID

或更常见的书面（因为2左联接是可交换）

FROM tblUsers 
LEFT JOIN tblArtworkTemplates 
    ON tblUsers.id = tblArtworkTemplates.editPingUserID 
LEFT JOIN tblSpecifications 
    ON tblArtworkTemplates.specID = tblSpecifications.id

来源

2011-02-23 10:48:08 RichardTheKiwi

添加连接时SQL行消失

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