SQL update make fields match

I want to use an SQL update statement to make a field in a file match a
field in the associated file record.  A crib sheet I found online shows 2
ways to do it:

update TableOne
    inner join TableTwo on TableOne.commonID = TableTwo.commonID 
    set TableOne.field1 = TableTwo.fieldX

Or:

update TableOne, TableTwo
    set TableOne.field1 = TableTwo.fieldX
    where TableOne.commonID = TableTwo.commonID

Is there a preference in picking one of these?  For example, the 2nd one
says "update" for both table names even though only one is actually being
updated.  Will there be some inefficiency here because of that?  Like some
unneeded lock on the file?  Or is the SQL engine smart enough that it will
"Read Everything Before Doing Anything" and handle it the same as the first?

Thanks for any insight.