用户定义函数中不能有动态sql。必须编写存储过程。下面的代码适用于任何表。但是，我建议您对以下程序进行适当的错误处理和其他操作。
数据设置

CREATE TABLE studentPercentage(studentId int, Fname varchar(30), LName varchar(30),
Age tinyint, city varchar(30))

insert into studentPercentage 
values (1 ,'KHALID', 'SMITH' ,  25   ,'LA'),
(2 ,'ADAM',     NULL  , NULL ,'NY'),
(3 ,'SARA',      'KAMAL' ,   23  ,Null),
(4 ,Null,       Null , Null  ,Null);

程序定义

CREATE PROCEDURE dbo.NULL_CALC
@tableName sysname,
@Idcolumn sysname,
@IdValue INT
AS
BEGIN
DECLARE @percentagestmt VARCHAR(max) = 'SELECT ('
DECLARE @countOfColumns INT = (SELECT COUNT(c.name) FROM
sys.tables as t
inner join sys.columns as c
on c.object_id = t.object_id
WHERE t.name = @tableName)

SELECT @percentagestmt += 'CASE WHEN '+ c.name + ' IS NOT NULL THEN 1 ELSE 0 END +'
FROM sys.tables as t
inner join sys.columns as c
on c.object_id = t.object_id
WHERE t.name = @tableName

SET @percentagestmt = LEFT(@percentageStmt,LEN(@percentagestmt) -1)

SET @percentagestmt += ') * 100 /' + CAST(@countOfColumns AS VARCHAR(10)) + ' AS RowNullPercentage FROM ' + @tableName + ' WHERE ' + @Idcolumn + '=' + cast(@Idvalue as varchar(10))

EXEC(@percentagestmt)
END

过程调用

EXEC dbo.NULL_CALC 'StudentPercentage','StudentId',1

结果集

+-------------------+
| RowNullPercentage |
+-------------------+
|               100 |
+-------------------+

你可以总结一下 CASE 此处的表达式用于查找百分比：

SELECT
    ID_STUDENT,
    100.0 * (CASE WHEN FNAME IS NULL THEN 1 ELSE 0 END +
             CASE WHEN LNAME IS NULL THEN 1 ELSE 0 END +
             CASE WHEN AGE   IS NULL THEN 1 ELSE 0 END +
             CASE WHEN CITY  IS NULL THEN 1 ELSE 0 END) / 4 AS pct_null
FROM STUDENT;

演示