如果 SQL 服务器 CASE 值为 NULL，则不 return 任何内容

Question

我有一个函数，可以根据特定条件 return 将多行数据与一列合并。

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 table 中有 Fruits 和 Vegetable 的值时，一切都很好。但是，如果前两种情况的值不存在，则输出 returned（来自最后 3 个查询）是

NULL
NULL
NULL

有什么方法可以避免那些 NULL 和 return 与前两个查询没有任何相似之处。

Answer 1

使用 COALESCE 替换 NULL 值。

https://msdn.microsoft.com/en-us/library/ms190349(v=sql.110).aspx

Answer 2

我绝不期望这是已确认的答案，我发布此内容只是为了向您展示对上述评论的答复：

 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

Answer 3

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

如果 SQL 服务器 CASE 值为 NULL，则不 return 任何内容

To not return anything if SQL Server CASE value is NULL

sql-server

function

sql-server-2008

table-valued-parameters