有那位Sql好手能够优化这段查询呢

有那位Sql高手能够优化这段查询呢？
现在有数据如下：
Department (部门表)部门表这个表采用树形结构
GuidCode         DepName        ParentGuid
    1             总部               0
    2             分部1              1
    3             分部2              1
    4             分部3              2
    5             分部4              2
    6             分部5              3
    7             分部6              3




Users（员工表）                  (本字段和上面的部门表关联，表示员工所属部门)
GuidCode          UserName       DepartmentGuid
   0                 老大               1
   1                 小一               3
   2                 小二               3
   3                 小三               2
   4                 小四               2
   5                 小五               6
   6                 小刘               6


Orders（订单表）                   (本字段和上面的员工表关联，表示这样订单的生成员工是谁)
GuidCode          OrderName        UserGuid             
   0                 订单1             1
   1                 订单2             1