谁能告诉我这有什么问题？我实际上试图在表中搜索空值，如果可能的话，建议我这样做的有效方法

Question

CREATE FUNCTION UDF_MALEEMPLOYEES(@GENDER NVARCHAR(4))
RETURNS TABLE
AS RETURN
IF (@GENDER='NULL')
(SELECT CONCAT(FIRSTNAME, CASE WHEN MIDDLENAME IS NULL THEN ' ' ELSE ' ' +MIDDLENAME+' ' END,LASTNAME) 
AS FULLNAME, CAST(BIRTHDATE AS DATE) AS BIRTHDATE,GENDER FROM PERSON.PERSON
A INNER JOIN [Sales].[vPersonDemographics] B ON A.BUSINESSENTITYID = B.BUSINESSENTITYID 
WHERE GENDER IS NULL)
ELSE
(SELECT CONCAT(FIRSTNAME, CASE WHEN MIDDLENAME IS NULL THEN ' ' ELSE ' ' +MIDDLENAME+' ' END,LASTNAME) 
AS FULLNAME, CAST(BIRTHDATE AS DATE) AS BIRTHDATE,GENDER FROM PERSON.PERSON
A INNER JOIN [Sales].[vPersonDemographics] B ON A.BUSINESSENTITYID = B.BUSINESSENTITYID 
WHERE GENDER =@GENDER)

Answer 1

Null不能等于null。您必须使用IS NULL，如下所示

CREATE FUNCTION UDF_MALEEMPLOYEES(@GENDER NVARCHAR(4))
RETURNS TABLE
AS RETURN
IF (@GENDER IS NULL)
(SELECT CONCAT(FIRSTNAME, CASE WHEN MIDDLENAME IS NULL THEN ' ' ELSE ' ' +MIDDLENAME+' ' END,LASTNAME) 
AS FULLNAME, CAST(BIRTHDATE AS DATE) AS BIRTHDATE,GENDER FROM PERSON.PERSON
A INNER JOIN [Sales].[vPersonDemographics] B ON A.BUSINESSENTITYID = B.BUSINESSENTITYID 
WHERE GENDER IS NULL)
ELSE
(SELECT CONCAT(FIRSTNAME, CASE WHEN MIDDLENAME IS NULL THEN ' ' ELSE ' ' +MIDDLENAME+' ' END,LASTNAME) 
AS FULLNAME, CAST(BIRTHDATE AS DATE) AS BIRTHDATE,GENDER FROM PERSON.PERSON
A INNER JOIN [Sales].[vPersonDemographics] B ON A.BUSINESSENTITYID = B.BUSINESSENTITYID 
WHERE GENDER =@GENDER)

Answer 2

当与NULL比较时，你使用IS NULL，而不是='NULL'，因为最后一个是varchar文字。

您还可以使您的功能更容易，更易于维护，如下所示：

CREATE FUNCTION UDF_MALEEMPLOYEES(@GENDER NVARCHAR(4))
RETURNS TABLE
AS RETURN
SELECT 
    CONCAT(FIRSTNAME, CASE WHEN MIDDLENAME IS NULL THEN ' ' ELSE ' ' +MIDDLENAME+' ' END,LASTNAME) AS FULLNAME, 
    CAST(BIRTHDATE AS DATE) AS BIRTHDATE,
    GENDER 
FROM 
    PERSON.PERSON A 
    INNER JOIN [Sales].[vPersonDemographics] B ON A.BUSINESSENTITYID = B.BUSINESSENTITYID 
WHERE 
    ISNULL(GENDER, '') = ISNULL(@GENDER, '')