如何编写一个 select inside case 语句 [英] How to write a select inside case statement

问题描述

我有一个存储过程，它在 select 语句中包含一个 case 语句.

I have a stored procedure that contains a case statement inside a select statement.

select Invoice_ID, 'Unknown' as Invoice_Status, 
case when Invoice_Printed is null then '' else 'Y' end as Invoice_Printed, 
case when Invoice_DeliveryDate is null then '' else 'Y' end as Invoice_Delivered, 
case when Invoice_DeliveryType <> 'USPS' then '' else 'Y' end as Invoice_eDeliver, 
Invoice_ContactLName+', '+Invoice_ContactFName as ContactName, 
from dbo.Invoice
left outer join dbo.fnInvoiceCurrentStatus() on Invoice_ID=CUST_InvoiceID 
where CUST_StatusID= 7 
order by Inv_Created  

在行 case when Invoice_DeliveryType <>'USPS' then '' else 'Y' 结尾为 Invoice_eDeliver

我需要检查有效的电子邮件地址(如果电子邮件有效，则显示 Y，否则显示 N).

I need to check for a valid email address (if email is valid, display Y, else display N).

所以这行会写成:

if Invoice_DeliveryType <>'USPS' then '' else (If ISNULL(Select emailaddr from dbo.Client Where Client_ID = SUBSTRING(Invoice_ID, 1, 6)), 'Y', 'N')

如何写出这个查询?

推荐答案

您可以使用 case 来做到这一点.我认为以下是您想要的逻辑:

You can do this with a case. I think the following is the logic you want:

(case when Invoice_DeliveryType <> 'USPS' then ''
      when exists (Select 1
                   from dbo.Client c
                   Where c.Client_ID = SUBSTRING(i.Invoice_ID, 1, 6) and
                         c.emailaddr is not null
                  )
      then 'Y'
      else 'N'
 end)

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