sql - SQL“NOT IN”由于某种原因无法正常工作..？

Question

以下 SQL 语句不起作用：

SELECT  stock.IdStock
        ,stock.Descr       
FROM    [Inventory].[dbo].[Stock] stock
WHERE   stock.IdStock NOT IN
        (SELECT foreignStockId FROM
         [Subset].[dbo].[Products])

Answer 1

可能返回一个NULL. 尝试

SELECT  stock.IdStock
        ,stock.Descr       
FROM    [Inventory].[dbo].[Stock] stock
WHERE   stock.IdStock NOT IN
        (SELECT foreignStockId FROM
         [Subset].[dbo].[Products]
         WHERE foreignStockId IS NOT NULL )

对于这种类型的查询，我通常使用 NOT EXISTS

SELECT stock.idstock,
       stock.descr
FROM   [Inventory].[dbo].[Stock] stock
WHERE  NOT EXISTS (SELECT *
                   FROM   [Subset].[dbo].[Products] p
                   WHERE  p.foreignstockid = stock.idstock)

Answer 2

最可能

SELECT foreignStockId FROM
         [Subset].[dbo].[Products]

查询返回至少一个 NULL 值

尝试存在

SELECT  stock.IdStock
        ,stock.Descr       
FROM    [Inventory].[dbo].[Stock] stock
WHERE   NOT EXISTS
        (SELECT * FROM [Subset].[dbo].[Products] 
         where stock.IdStock =foreignStockId )