This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You can perform an update into using a select, but I think he's talking about modifying the data coming from the select statement artibitrarily. In that case you have to create a new statement to the database an execute an UPDATE sql command separately from your SELECT query. That's the cleaner/better way to do it anyway.
For example, you may need to make changes to a dozen records, rather than 12 separate update calls, mark the records during the select you need to change and then update them all in a single update statement after all the records have been read.