MySQL

You'll get the best performance if you forget the where clause and place all conditions in the ON expression.

I think this is because the query first has to join the tables then runs the where clause on that, so if you can reduce what is required to join then that's the fasted way to get the results/do the udpate.

Example

Scenario

You have a table of users. They can log in using their username or email or account_number. These accounts can be active (1) or inactive (0). This table has 50000 rows

You then have a table of users to disable at one go because you find out they've all done something bad. This table however, has one column with usernames, emails and account numbers mixed. It also has a "has_run" indicator which needs to be set to 1 (true) when it has been run

Query

UPDATE users User
    INNER JOIN
        blacklist_users BlacklistUser
        ON
        (
            User.username = BlacklistUser.account_ref
            OR
            User.email = BlacklistedUser.account_ref
            OR
            User.phone_number = BlacklistUser.account_ref
            AND
            User.is_active = 1
            AND
            BlacklistUser.has_run = 0
        )
    SET
        User.is_active = 0,
        BlacklistUser.has_run = 1;

Reasoning

If we had to join on just the OR conditions it would essentially need to check each row 4 times to see if it should join, and potentially return a lot more rows. However, by giving it more conditions it can "skip" a lot of rows if they don't meet all the conditions when joining.

Bonus

It's more readable. All the conditions are in one place and the rows to update are in one place

The simplest way is to use the Common Table Expression (CTE) introduced in SQL 2005

with cte as
(select u.assid col1 ,s.assid col2 from ud u inner join sale s on u.id = s.udid)
update cte set col1=col2

Try this one, I think this will works for you

update ud

set ud.assid = sale.assid

from ud 

Inner join sale on ud.id = sale.udid

where sale.udid is not null

For SQLite use the RowID property to make the update:

update Table set column = 'NewValue'
where RowID = 
(select t1.RowID from Table t1
join Table2 t2 on t1.JoinField = t2.JoinField
where t2.SelectValue = 'FooMyBarPlease');