I'm trying to write a query that will take unsubscribes from a child BU and write into a shared DE at the parent level. I know how to find the unsubscribes, but I'm trying to write into a DE field where we store the "status" so I thought I would use a SET statement (SET brand\_subscribed = 'false') but I keep getting an error at the SET statement.

Can I use a SET statement in a Query in Marketing Cloud?

I don't want to assign a default value of FALSE as I don't want to accidentally mark someone as unsubscribed if they are in another business unit (all unsubs for the parent are being written into the shared DE).