Question

declare @T table
(
  ID int identity primary key, 
  FBK_ID BIGINT null, 
  TWT_ID BIGINT null,
  LNK_ID NVARCHAR(50) null
);

每条记录只能有FBK_ID或TWT_ID或LNK_ID。没有记录在这些字段上有多个值。

因此，主要有些记录会有FacebookID值，有些记录会有TwitterID，有些记录会有LinkedInID。

问题：
什么是最快，最干净的方法呢？

选择ID，从@T

输入

....其中Type是nvarchar（10）等于'Facebook'或'Twitter'或'LinkedIn'，具体取决于谁有价值？

Answer 1

你可以这样做：

select 
ID ,
case when FBK_ID is not null then FBK_ID
     when TWT_ID is not null  then  TWT_ID 
else LNK_ID end as LinkID
from @t 
where <rest of your conditions if any>

您将获取特定社交网络的ID和其中一个链接IDS。此外，如果您想知道LinkID返回的社交网络属于哪种社交网络，您可以添加一个额外的列：

select 
ID ,
case when FBK_ID is not null then FBK_ID,
     when TWT_ID is not null  then  TWT_ID 
else LNK_ID end as LinkID,
case when FBK_ID is not null then 'F'
     when TWT_ID is not null  then  'T'
else 'L' end as LinkIDFrom
from @t 
where <rest of your conditions if any>

Answer 2

每条记录只能有FBK_ID或TWT_ID或LNK_ID。没有记录在这些字段上有多个值。

首先修复你的桌子：

DECLARE @T TABLE
(
  ID INT IDENTITY PRIMARY KEY, 
  FBK_ID BIGINT NULL, 
  TWT_ID BIGINT NULL,
  LNK_ID NVARCHAR(50) NULL, 
  CHECK (
         (FBK_ID IS NOT NULL AND TWT_ID IS NULL AND LNK_ID IS NULL)
         OR (FBK_ID IS NULL AND TWT_ID IS NOT NULL AND LNK_ID IS NULL)
         OR (FBK_ID IS NULL AND TWT_ID IS NULL AND LNK_ID IS NOT NULL)
        )
);

最快，最干净的方法是什么？

这对我来说写得很快，使用复制+粘贴，看起来很干净：

SELECT ID, CAST('Facebook' AS NVARCHAR(10)) AS Type
  FROM @T
 WHERE FBK_ID IS NOT NULL
UNION
SELECT ID, CAST('Twitter' AS NVARCHAR(10)) AS Type
  FROM @T
 WHERE TWT_ID IS NOT NULL
UNION
SELECT ID, CAST('LinkedIn' AS NVARCHAR(10)) AS Type
  FROM @T
 WHERE LNK_ID IS NOT NULL;

多列上的TSQL CASE

2 个答案: