如何在NOT IN子句中使用select语句中的字符串列表

Question

我想构建一个姓氏列表，以便从第二个select语句的结果中过滤出类似的内容（不这样做）

DECLARE @ExcludedList VARCHAR(MAX) 
SET @ExcludedList = (SELECT TOP 20 Lastname 
FROM dbo.Subscribers 
where [Firstname] = 'Dave') 

SELECT [Firstname], Count([Firstname]) as [Count] from Subscribers 
WHERE [Lastname] not in (@ExcludedList) 

Answer 1

如果你需要使用一个变量，那么它必须是一个表变量：

DECLARE @ExcludedList TABLE (Lastname VARCHAR(MAX)) 

INSERT INTO @ExcludedList 
SELECT TOP 20 Lastname 
FROM dbo.Subscribers 
WHERE [Firstname] = 'Dave' 

SELECT [Firstname], Count([Firstname]) AS [Count] 
FROM Subscribers 
WHERE [Lastname] NOT IN (SELECT Lastname FROM @ExcludedList) 

Answer 2

为什么你不能做到这一点直接像

SELECT [Firstname], Count([Firstname]) as [Count] from Subscribers 
WHERE [Lastname] not in (SELECT TOP 20 Lastname 
FROM dbo.Subscribers where [Firstname] = 'Dave') 

好吧，我不知道你实际上是试图实现，但考虑使用table variable和使用如下

DECLARE @ExcludedList table(lastname varchar(30)); 
insert into @ExcludedList 
SELECT TOP 20 Lastname 
FROM dbo.Subscribers where [Firstname] = 'Dave'; 

SELECT [Firstname], Count([Firstname]) as [Count] from Subscribers 
WHERE [Lastname] not in (select lastname from @ExcludedList);