Question

如何在MS Access SQL查询中编写If else Ladder，使用Recordset编写不在代码中。

我有这样的条件：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' 
AND SpecialistCode = 'C4535421' AND WeekNum = 1

它会给出任何值，如果没有，我想运行这个查询：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' 
AND SpecialistCode = 'C4535421' AND (WeekNum is Null or WeekNum = '')

它会给出任何值，如果没有，我想运行这个查询：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' 
AND (SpecialistCode is null or SpecialistCode ='') AND WeekNum = 1

它会给出任何值，如果没有，我想运行这个查询：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' 
AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum is Null or WeekNum = '')

它会给出任何值，如果没有，我想运行这个查询：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE (SpecialityCode is null 
or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='') AND WeekNum = 1

它会给出任何值，如果没有，我想运行这个查询：

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE (SpecialityCode is null 
or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='')      
AND (WeekNum is Null or WeekNum = '')

基本上，我在查询中给出3个条件，如果没有找到该条件的记录，那么我将逐步替换空值或null的条件。目前我正在使用记录集，意味着检查记录集的计数，如果为0，则用下一个条件填充记录集，依此类推。但是这种方法需要花费很多时间，因为这本身就是围绕100多个记录循环完成的。所以我能做到的任何其他方式都可以在一个查询中吗？

Answer 1

考虑嵌套的IIF语句。注意反转的条件层次结构：

SELECT min(IIF((SpecialityCode is null or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum is Null or WeekNum = ''), 
ThreshodValue,
IIF((SpecialityCode is null or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum = 1),
ThresholdValue,
IIF(SpecialityCode = '130' AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum is Null or WeekNum = ''),
ThresholdValue,
IIF(SpecialityCode = '130' AND (SpecialistCode is null or SpecialistCode ='') AND WeekNum = 1, 
ThresholdValue,
IIF(SpecialityCode = '130' AND SpecialistCode = 'C4535421' AND (WeekNum is Null or WeekNum = ''), 
ThresholdValue,
IIF(SpecialityCode = '130' AND SpecialistCode = 'C4535421' AND WeekNum = 1, 
ThresholdValue, 0)))))))
FROM tbl_threshold;

或者，您可以考虑一个Union查询，其中如果将排除没有值的select语句，并且union（vs union all）会阻止重复。但是可能你想在union查询中返回id和thresholdvalues，并在另一个查询中使用min（）返回聚合联合查询。

SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' AND SpecialistCode = 'C4535421' AND WeekNum = 1
UNION
SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' AND SpecialistCode = 'C4535421' AND (WeekNum is Null or WeekNum = '')
UNION
SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' AND (SpecialistCode is null or SpecialistCode ='') AND WeekNum = 1
UNION
SELECT min(ThresholdValue) FROM tbl_Threshold WHERE SpecialityCode = '130' AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum is Null or WeekNum = '')
UNION
SELECT min(ThresholdValue) FROM tbl_Threshold WHERE (SpecialityCode is null or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='') AND WeekNum = 1
UNION
SELECT min(ThresholdValue) FROM tbl_Threshold WHERE (SpecialityCode is null or SpecialityCode ='') AND (SpecialistCode is null or SpecialistCode ='') AND (WeekNum is Null or WeekNum = '');

如果Else Ladder在MS Access SQL查询中

1 个答案: