Postgres and multiple updates in one statement

Hi there

We have a function which runs a set of update clauses and we are considering putting all the update clauses into one statement.

I would like to understand how postgres handles multiple updates. If we were to send 5 update statements in one sql statement to the db would it:

Do 5 passes on the table, on each pass, retrieve the id then update the row

Do 1 pass to retrieve the 5 primary keys, then update all rows in parallel

Apart from saving on the overhead of having to open up 5 separate connections, what are the benefits to passing in multiple updates in one statement?

Many thanks,

Jamie