如何从我的结果中删除 CASE 语句？

Posted 2023-03-29

【中文标题】如何从我的结果中删除 CASE 语句？

【英文标题】：How to remove CASE statements from my results?

【发布时间】：2021-12-09 06:20:47

【问题描述】：

我正在编写一个查询来返回一些信息，但存储过程不会在页面中返回结果，因为这些值与表定义不匹配。我理解这个错误。但我使用 case 语句根据字段进行过滤（无论是否收到 t.TimeCallWasReceived）。当我这样做时，它允许 sp 在用户检查数据库更改或使用 signalR 检测数据库更改时运行。我不希望 CASE 语句成为我结果的一部分。我知道我可以更改页面或临时表，但我想知道我是否可以在 t-sql 中执行任何操作以在所述结果中不包含 case 语句的情况下返回结果。查询如下。

SELECT DISTINCT
       c.Num,
       'Notified for pickup ' + (CONVERT(varchar(30), c.ServiceCalled, 100)) + '. Number ' + c.Num AS Issue,
       RTRIM(c.NameFirst) + ' ' + RTRIM(c.NameLast) AS CusName,
       (CASE
             WHEN t.TimeCallWasReceived IS NULL THEN CONVERT(varchar(20), t.TimeCallWasReceived, 113)
             ELSE 'NO'
        END) AS CallReceivedAt
FROM tblCustomer c
     LEFT JOIN tblTransportation t ON t.Num = c.Num
WHERE t.TimeCallWasReceived IS NULL
  AND c.Type = 'Type1'
  AND c.ServiceCalled IS NOT NULL
  AND c.TransportNum IS NULL
  AND LEFT(c.Num, 2) <> 'CR'
  AND LEFT(c.Num, 2) <> 'TR'
  AND (c.Status <> 'Void'
    OR c.Status <> 'Closed')
  AND ((DATEDIFF(MINUTE, c.ServiceCalled, GETDATE())) > 180)
  AND c.Type <> 'VOID'
  AND c.Type <> 'NON'
  AND c.Type <> 'Walk-In'
  AND c.Type <> 'CFR'
  AND c.CaseType <> 'PAP'
  AND c.ServiceCalled >= DATEADD(DAY, -2, GETDATE())
ORDER BY c.Num DESC;

【问题讨论】：

仅供参考，这是一个CASE 表达式，而不是CASE 语句。

IIF (t.TimeCallWasReceived IS NULL, CONVERT(varchar(20), t.TimeCallWasReceived, 113), 'NO') AS CallReceivedAt

我真的不明白你在这里追求什么。如果您不希望结果中出现CASE 表达式定义的列，则将其从SELECT 中删除。为什么你不能这样做？

RE: "...但是存储过程不会在页面中返回结果，因为值与表定义不匹配..." 这句话很令人困惑，您在说什么“页面”和“表格”？就像在此之前有一整段解释/上下文丢失了。

条件是错误的WHEN t.TimeCallWasReceived IS NULL你不能转换它，在这种情况下应该返回'NO'。

【参考方案1】：

--1. Since the WHERE clause has `t.TimeCallWasReceived IS NULL`, you will see only ---'NO' in the CallReceivedAt result column.
--2. Since the WHERE clause has `c.Type = 'Type1'`, it makes unnecessary to look for 

c.Type <> 'VOID'
c.Type <> 'NON'
c.Type <> 'Walk-In'
c.Type <> 'CFR'

--because they are exclusive for the rest of the values different than 'Type1'.
--3. I don't see a way to get rid of the CASE
--    Perhaps you like this way better:
    
CASE ISNULL(t.TimeCallWasReceived, '')
     WHEN '' THEN CONVERT(varchar(20), t.TimeCallWasReceived, 113)
             ELSE 'NO'
END

【讨论】：

又一次打了就跑