Sql server 如果SQL Server案例值为NULL，则不返回任何内容

我有一个函数，它根据特定条件返回一列多行数据

ALTER FUNCTION [dbo].[GetFavoriteFruits]
(   
    @FruitId uniqueidentifier
)
RETURNS TABLE 
AS
RETURN 
(
    Select Name FROM Fruits WHERE FruitID = @FruitId
    UNION ALL
    Select Name FROM Vegetables WHERE VegetableID = @FruitId
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) THEN 'Fruit Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Vegetable Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) OR EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Either Fruit or Vegetable exists'
    END
)

当桌上有水果和蔬菜的价值时，一切都很好。但是，如果前两种情况的值不存在，则返回的输出（来自最后3个查询）是

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有没有一种方法可以避免这些空值，并且不返回与前两个查询类似的任何内容。

使用COALESCE替换空值

---

使用合并替换空值

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我绝不希望这是一个确定的答案，我发布这篇文章只是为了向您展示对您上述评论的回答：

 ALTER FUNCTION [dbo].[GetFavoriteFruits]
(   
    @FruitId uniqueidentifier
)
RETURNS TABLE 
AS
RETURN 
(
    SELECT x.Name FROM (
    Select Name FROM Fruits WHERE FruitID = @FruitId
    UNION ALL
    Select Name FROM Vegetables WHERE VegetableID = @FruitId
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) THEN 'Fruit Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Vegetable Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) OR EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Either Fruit or Vegetable exists'
    END
) ) AS x
WHERE x.Name IS NOT NULL

---

我决不希望这是一个确定的答案，我发布这篇文章只是为了向您展示对您上述评论的回答：

 ALTER FUNCTION [dbo].[GetFavoriteFruits]
(   
    @FruitId uniqueidentifier
)
RETURNS TABLE 
AS
RETURN 
(
    SELECT x.Name FROM (
    Select Name FROM Fruits WHERE FruitID = @FruitId
    UNION ALL
    Select Name FROM Vegetables WHERE VegetableID = @FruitId
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) THEN 'Fruit Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Vegetable Exists'
    END
    UNION ALL
    Select
    CASE
    WHEN EXISTS(Select Name FROM Fruits WHERE FruitID = @FruitId) OR EXISTS(Select Name FROM Vegetables WHERE VegetableID = @FruitId) THEN 'Either Fruit or Vegetable exists'
    END
) ) AS x
WHERE x.Name IS NOT NULL

---

您将所有结果合并在一起，因此您可以将您拥有的内容放入子查询中，然后使用where子句查询这些结果以过滤空值，有很多更好的方法，但为了巩固你的成果…@RyanWilson你能告诉我如何使用外部查询过滤空值吗？我发布了一个答案，作为如何使用外部查询的示例。你将所有结果合并在一起，这样你就可以将你拥有的内容生成子查询，然后使用where子句查询这些结果以过滤空值，有很多更好的方法，但只是为了建立你所得到的…@RyanWilson你能告诉我如何使用外部查询过滤空值吗？发布了一个答案作为如何使用外部查询的示例。RyanWilson是正确的。有更好的方法可以做到这一点。加上1对你来说@kalaolaniRyan Wilson是正确的。有更好的方法可以做到这一点。加上你的1@kalaolani

...
SELECT 'Fruit Exists'
WHERE EXISTS(Select 1 FROM Fruits WHERE FruitID = @FruitId)
...