MS Access SQL查询中的If-Else梯形图

如何使用记录集在MS Access SQL查询中编写If-else梯形图，而不是在代码中编写

我有这样的条件：

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

它将给出任何值，如果没有，我想运行此查询：

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

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

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

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

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

它将给出任何值，如果没有，我想运行此查询：

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

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

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

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

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

它将给出任何值，如果没有，我想运行此查询：

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

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

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

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

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

它将给出任何值，如果没有，我想运行此查询：

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

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

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

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

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

它将给出任何值，如果没有，我想运行此查询：

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

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

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

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

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，我在查询中给出了3个条件，如果没有找到该条件的记录，那么我将逐步用空值或null替换条件。目前，我正在使用记录集进行此操作，这意味着检查记录集的计数，若为0，则使用下一个条件填充记录集，依此类推。但是这种方法花费了太多的时间，因为它本身是在一个超过100条记录的循环中完成的。因此，我可以用任何其他方法来实现这一点，可能是在一个查询中？

考虑一个嵌套的IIF语句。请注意条件的反向层次结构：

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;

可选地，您可以考虑一个联合查询，其中如果不包含任何值的SELECT语句，则UNION（VS UNIONALL）将防止重复。但您可能希望在联合查询中返回ID和阈值，并在另一个查询中使用min（）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 = '');

---

考虑一个嵌套的IIF语句。请注意条件的反向层次结构：

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;

可选地，您可以考虑一个联合查询，其中如果不包含任何值的SELECT语句，则UNION（VS UNIONALL）将防止重复。但您可能希望在联合查询中返回ID和阈值，并在另一个查询中使用min（）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 = '');

---

你能用外行的话解释一下你想做什么吗？必须有另一种方法来做到这一点，不同于多次测试多个条件。@PaulFrancis我已经在我的线程底部用简单的语言解释了它。首先，我检查表中是否有包含所有3个条件的行，如果没有，那么我一次忽略第三个条件，然后根据其余2个条件进行检查，如果也没有找到数据，那么我忽略第二个条件，只检查第一个条件。因为这三列中可能都有值的数据。为了提供另一种选择，我认为我们首先需要知道这种方法的目的。你能用外行的术语解释一下你想做什么吗？必须有另一种方法来做到这一点，不同于多次测试多个条件。@PaulFrancis我已经在我的线程底部用简单的语言解释了它。首先，我检查表中是否有包含所有3个条件的行，如果没有，那么我一次忽略第三个条件，然后根据其余2个条件进行检查，如果也没有找到数据，那么我忽略第二个条件，只检查第一个条件。因为这三列中可能都有值的数据。为了提供另一种选择，我认为我们首先需要知道这种方法的目的。你能用外行的术语解释一下你想做什么吗？必须有另一种方法来做到这一点，不同于多次测试多个条件。@PaulFrancis我已经在我的线程底部用简单的语言解释了它。首先，我检查表中是否有包含所有3个条件的行，如果没有，那么我一次忽略第三个条件，然后根据其余2个条件进行检查，如果也没有找到数据，那么我忽略第二个条件，只检查第一个条件。因为可能有数据在这三列中都有值，或者没有。为了提供一个替代方案，我认为我们首先需要知道这种方法的目的。