如何确定何时使用右连接/左连接或内部连接，或者如何确定哪张表在哪一边？?mysql

我知道加入的使用情况，但有时我遇到这样的情况时，我不能决定哪些加入将是合适的，一个向左或向右。

这是我卡住的查询。

SELECT  count(ImageId) as [IndividualRemaining],
            userMaster.empName AS ID#,
            CONVERT(DATETIME, folderDetails.folderName, 101) AS FolderDate,
            batchDetails.batchName AS Batch#,
            Client=@ClientName,
            TotalInloaded = IsNull(@TotalInloaded,0),
            PendingUnassigned = @PendingUnassigned,
            InloadedAssigned =     IsNull(@TotalAssigned,0),
            TotalProcessed = @TotalProcessed,
            Remaining = @Remaining
    FROM
            batchDetails
                Left JOIN  folderDetails ON batchDetails.folderId = folderDetails.folderId
                Left JOIN  imageDetails ON batchDetails.batchId = imageDetails.batchId
                Left JOIN  userMaster ON imageDetails.assignedToUser = userMaster.userId

    WHERE   folderDetails.ClientId =@ClientID and verifyflag='n'
            and folderDetails.FolderName IN (SELECT convert(VARCHAR,Value) FROM dbo.Split(@Output,','))
            and userMaster.empName <> 'unused'

    GROUP BY userMaster.empName, folderDetails.folderName, batchDetails.batchName

    Order BY folderDetails.Foldername asc