首先注释初始 BEGIN 块中的@USERNAME 声明

First comment the @USERNAME declaration in the initial BEGIN block

 -- DECLARE @USERNAME varchar(110)

然后像在 SELECT * INTO 块中一样处理 USERNAME 的 NULL 值

then handle the NULL value for the USERNAME as in the SELECT * INTO block

 ISNULL(b.first_Name, '') + ' ' + ISNULL(b.last_name, '') AS USERNAME

然后在 CURSOR 中添加 @USERNAME 为

Then add the @USERNAME in the CURSOR as

DECLARE Cur_1 CURSOR
        FOR SELECT CUser_id, User_Id, USERNAME FROM #temptable

            OPEN Cur_1
                    DECLARE @CUser_id INT
                    DECLARE @User_Id INT
                    DECLARE @USERNAME VARCHAR (200) -- can set your required length
                    FETCH NEXT FROM Cur_1 
                    INTO @CUser_id, @User_Id

那么 @USERNAME 就不会抛出 NULL 错误

Then the @USERNAME won't throw the NULL error

更新:根据您的评论，我更新了答案:

UPDATE: Based on your comments, I updated the answer:

所以您想根据 U_datetime >= @As_ONDATE 条件获取 @USERNAME.

So you want to get the @USERNAME based on the U_datetime >= @As_ONDATE condition.

因此，使用您现有的代码并在 CURSOR 中再添加一个块以获取 @USERNAME 值，就像 SELECT @REPORTDATE = U_datetime FROM inward_doc_tracking_trl where U_datetime >= @As_ONDATE代码>

So use your existing code and add one more block inside the CURSOR for getting the @USERNAME value as after the SELECT @REPORTDATE = U_datetime FROM inward_doc_tracking_trl where U_datetime >= @As_ONDATE

SELECT @USERNAME = ISNULL(b.first_Name, '') + ' ' + ISNULL(b.last_name, '') -- no need of column alias here
FROM inward_doc_tracking_trl a 
INNER JOIN user_mst b on a.CUser_id = b.mkey 
WHERE a.U_datetime >= @As_ONDATE