Select * from vwOutHouseDsp
where iDocStatus<=100 and dDocDate>=@tdBDate and dDocDate<=@tdEDate
and (cDocType='销售发货' or cDocType='销售退货')
and WhSysCode=case when @tcWhSysCode='' then WhSysCode else @tcWhSysCode End
and ISysCode=case when @tcISysCode='' then ISysCode else @tcISysCode End
and IBSysCode=case when @tcIBSysCode='' then IBSysCode else @tcIBSysCode
以上这句在WHERE上使用CASE后查速度就变得很慢了，如果把
and WhSysCode=case when @tcWhSysCode='' then WhSysCode else @tcWhSysCode End
and ISysCode=case when @tcISysCode='' then ISysCode else @tcISysCode End
and IBSysCode=case when @tcIBSysCode='' then IBSysCode else @tcIBSysCode
这几句去掉，速度就正常了，怎么会这样呢？
另外，如果不用CASE，这种情况的条件查询怎样解决比较好呢？
