SQL 2000 NED表具有指向SIGN表的外键NED.RowID到SIGN.RowID
SIGN表具有指向NED表的外键SIGN.SignID到NED.SignID
RowID和SignID是作为GUID的群集主键（不是我的选择）
WHERE子句是：

FROM
    [SIGN] A   
    INNER JOIN NED N ON A.SIGNID = N.SIGNID  
    INNER JOIN Wizard S ON A.WizardID = S.WizardID   
    INNER JOIN [Level] SL ON N.LevelID = SL.LevelID  
    LEFT JOIN Driver DSL ON SL.LevelID = DSL.LevelID  
        AND DSL.fsDeptID = @fsDeptID  
    INNER JOIN [Character] ET ON S.CharacterID = ET.CharacterID  
    INNER JOIN Town DS ON A.TownID = DS.TownID   
WHERE  
    (A.DeptID = @DeptID OR   
    S.DeptID = @DeptID  
    AND   
    A.[EndTime] > @StartDateTime AND A.[StartTime] < @EndDateTime  
    AND   
    A.NEDStatusID = 2

为什么在SIGN表上对此查询有INDEX SCAN？什么会导致对聚集索引进行索引扫描？谢谢