Question

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tbl Artwork Templates.editPing UserID为null时，tblusers join会导致行消失。我使用了错误的连接类型吗？

Answer 1

也许尝试左外连接..或右外连接..

Wikipedia了解有关加入

的信息

Answer 2

试试这个，你的加入是错误的。

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)

Answer 3

这取决于你的目标。

如果你总是想要来自tblUsers的记录，但是只有来自的数据来自Template + Specification的数据（换句话说，如果模板没有规范，你就不关心模板了），使用此

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

如果您总是需要来自tblUsers的记录，但是来自模板的数据（如果可用），然后来自规范（如果可用）（换句话说，如果模板可用没有规范，则无论如何从模板记录中获取数据） ，然后使用此

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

或更常见的写法（因为2个左连接是可交换的）

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

添加连接时SQL行消失

3 个答案: