But there is no need to add a from clause as it was working fine.

See the code below:

--my table payment_details structure is

DECLARE @payment_details TABLE

(

payment_id INT PRIMARY KEY CLUSTERED NOT NULL

,payment_code INT NULL

);

INSERT INTO @payment_details (payment_id)

VALUES (1),(2),(3),(4)

UPDATE @payment_details

SET payment_code =payment_id

WHERE payment_code IS NULL

SELECT

*

FROM @payment_details

Result:

payment_id payment_code

----------- ------------

1 1

2 2

3 3

4 4

Kindly, share the exact error..