update month column from date column in the same table SQL Server

Question

i have a data that has a transaction Date [DATETIME] and i'm trying to have a query that go to each transaction row and get the month and year based on the transaction_Date and update the month column for big number of tranasction.

example

ID      Trans_Date              Month
01      01/01/2020              012020
02      02/01/2020              012020
03      01/05/2020              052020

any suggestions?

Answer 1

Do this using a computed column:

alter table t add month as (format(trans_date, 'MMyyyy'));

You can do something like this using an update . But that is silly. The values will not be correct on new rows or on updates to existing rows. With a computed column, the values are always correct.

You can, of course, express this as an update :

update t
    set month = format(trans_date, 'MMyyyy');

If some of the values are already correct, then add a where clause: where month <> format(trans_date, 'MMyyyy') .

Answer 2

Hi just managed to do it this way:

UPDATE [DB].[dbo].[TABLE] SET [MONTH]= FORMAT(TRANS_DATETIME,'yyyy0MM');