将SQL Server结果集转换为字符串

Question

我在SQL Server中得到的结果为

SELECT StudentId FROM Student WHERE condition = xyz

我得到的输出就像

StudentId
1236

7656

8990
........

存储过程的输出参数是@studentId字符串,我希望return语句为

1236, 7656, 8990.

如何在单个字符串中转换输出？

我正在返回单列[即.学生卡]

Answer 1

DECLARE @result varchar(1000)

SELECT @result = ISNULL(@result, '') + StudentId + ',' FROM Student WHERE condition = xyz

select substring(@result, 0, len(@result) - 1) --trim extra "," at end

Answer 2

测试一下:

 DECLARE @result NVARCHAR(MAX)

 SELECT @result = STUFF(
                        (   SELECT ',' + CONVERT(NVARCHAR(20), StudentId) 
                            FROM Student 
                            WHERE condition = abc 
                            FOR xml path('')
                        )
                        , 1
                        , 1
                        , '')

Answer 3

使用COALESCE功能:

DECLARE @StudentID VARCHAR(1000)
SELECT @StudentID = COALESCE(@StudentID + ',', '') + StudentID
FROM Student
WHERE StudentID IS NOT NULL and Condition='XYZ'
select @StudentID

Answer 4

这两个答案都是有效的,但不要忘记初始化变量的值,默认为NULL并使用T-SQL:

NULL + "Any text" => NULL

这是一个非常常见的错误,不要忘记它!

使用ISNULL功能也是个好主意:

SELECT @result = @result + ISNULL(StudentId + ',', '') FROM Student

Answer 5

使用该CONCAT函数可以避免转换错误：

DECLARE @StudentID VARCHAR(1000)
SELECT @StudentID = CONCAT(COALESCE(@StudentID + ',', ''), StudentID)
FROM Student
WHERE StudentID IS NOT NULL and Condition='XYZ'
select @StudentID