Question

我正在尝试加入三张桌子，我成功加入了两张桌子。

这个工作（两个表）

SELECT  ImportExportBadFile.ID, ImportExportSettingID,
    ImportExportBadFile.UserID,
    Coalesce(UserName,'') UserName  
    FROM
    ImportExportBadFile 
    LEFT OUTER JOIN Users HGSQLUsers ON ImportExportBadFile.UserID = HGSQLUsers.ID
    ORDER BY  ImportExportBadFile.DateTimeStamp DESC

UserName属于Users Table

现在，当我尝试添加另一个表时：

SELECT  ImportExportBadFile.ID, ImportExportSettingID,
    SETT.Name,
    ImportExportBadFile.UserID,
    Coalesce(UserName,'') HGSQLUsers.UserName  
    FROM
    ImportExportBadFile 
    LEFT OUTER JOIN Users HGSQLUsers ON ImportExportBadFile.UserID = HGSQLUsers.ID
    INNER JOIN ImportExportSettings SETT ON ImportExportBadFile.ImportExportSettingID = SETT.ID  
    ORDER BY  ImportExportBadFile.DateTimeStamp DESC

它给出了错误：＆＃34;＆＃39;附近的语法错误。＆＃39;。＆＃39;。＆＃34;在线：＆＃34;合并（用户名，＆＃39;＆＃39;）HGSQLUsers.UserName＆＃34;

如果我只写UserName它会给出

＆＃34;不明确的列名＆＃39;用户名＆＃39;。＆＃34;

帮助。

Answer 1

两个表中都可能存在UserName列，您需要指定从哪个表中选择UserName，如下所示

SELECT  ImportExportBadFile.ID, ImportExportSettingID,
    SETT.Name,
    ImportExportBadFile.UserID,
    Coalesce( HGSQLUsers.UserName  ,'') as "HGSQLUsers.UserName"
    FROM
    ImportExportBadFile 
    LEFT OUTER JOIN Users HGSQLUsers ON ImportExportBadFile.UserID = HGSQLUsers.ID
    INNER JOIN ImportExportSettings SETT ON ImportExportBadFile.ImportExportSettingID = SETT.ID
ORDER BY  ImportExportBadFile.DateTimeStamp DESC

错误"Incorrect syntax near '.'." at line :来自别名HGSQLUsers.UserName您可以在配额中使用它。

我还建议你为每个表使用别名，如下所示 - 对我来说更具可读性

SELECT  I.ID, I.ImportExportSettingID,
        SETT.Name,
        I.UserID,
       Coalesce( HGSQLUsers .UserName  ,'') as "HGSQLUsers.UserName"
FROM ImportExportBadFile I
LEFT OUTER JOIN Users HGSQLUsers ON I.UserID = HGSQLUsers.ID
INNER JOIN ImportExportSettings SETT ON I.ImportExportSettingID = SETT.ID  
ORDER BY  I.DateTimeStamp DESC

Answer 2

实际上这在试错中对我有用：

SELECT  ImportExportBadFile.ID, ImportExportSettingID,
    SETT.Name,
    ImportExportBadFile.UserID,
    Coalesce(HGSQLUsers.UserName,'')
    FROM
    ImportExportBadFile 
    INNER JOIN ImportExportSettings SETT ON ImportExportBadFile.ImportExportSettingID = SETT.ID  
    LEFT OUTER JOIN Users HGSQLUsers ON ImportExportBadFile.UserID = HGSQLUsers.ID
    ORDER BY  ImportExportBadFile.DateTimeStamp DESC

但是@Parado的答案更具体和解释。

谢谢。

＆＃39;附近的语法不正确。＆＃39;使用Coalesce时

2 个答案: