Question

我正在运行查询以根据位置，建筑物编号等选择审批者凭据。我想要为特定位置设置默认审批者，因此在表中创建一个条目，其中包含Site值和NULL AcctDept。结果集预计是一行。

以下是查询：

select distinct CS, Primary, Backup1, Backup2 
from Approvals 
where AcctDept = #ApprovalInformation.Account# 
            and Building = #ApprovalInformation.Building# 
            and Site = #ApprovalInformation.Site# 
            and AcctDept is not null 
            and Building is not null 
union 
select distinct CS, Primary, Backup1, Backup2 
from Approvals 
where AcctDept = #ApprovalInformation.Account# 
            and Site = #ApprovalInformation.Site# 
            and AcctDept is not null 
            and Building is null 

union select distinct CS, Primary, Backup1, Backup2 
from Approvals 
where Building = #ApprovalInformation.Building# 
            and Site = #ApprovalInformation.Site# 
            and AcctDept is null 
            and Building is not null 

union 
select distinct CS, Primary, Backup1, Backup2 
from Approvals 
where Site = #ApprovalInformation.Site# 
            and AcctDept is null 
            and Building is null 
and NOT EXISTS (
                    select * 
                    from Approvals 
                    where AcctDept = #ApprovalInformation.Account# 
                            and Building = #ApprovalInformation.Building# 
                            and Site = #ApprovalInformation.Site# 
                            and AcctDept is not null 
                            and Building is not null)

我的想法是，如果第一个SELECT返回一个值，则不需要默认值，NOT EXISTS语句将评估为false。（第一个选择只是复制/粘贴到最后一个语句的NOT EXISTS中）

但是，当我运行它时，它总是评估为TRUE。

我遗漏的NOT EXISTS的行为一定有什么意义吗？

Answer 1

select top 1 CS, Primary, Backup1, Backup2 
from Approvals 
where (AcctDept = #ApprovalInformation.Account# or AcctDept is null)
            and (Building = #ApprovalInformation.Building# or Building is null)
            and Site = #ApprovalInformation.Site# 
order by AcctDept, Building

oracle中的默认排序是asc，nulls last。使用前1个子句，这将为您提供一条记录，其中包含非空的AcctDept和Building（如果可用）。未经测试，因为没有提供SQLFiddle。

NOT EXISTS返回意外结果

1 个答案: