You could use a sqlexecuter transformer to execute statements on any database

As @david_r says, you could use a FeatureWriter transformer instead of a writer, then - as @arnovananrooij mentions - add a SQLExecutor to carry out an update.

The other solution is to use the writer parameter called SQL to Run After Write. You can put your SQL in there and it will run after the writer is complete.

To be honest, the FeatureWriter/SQLExecutor is a better way, because if the writer fails for some reason, you can choose not to run the SQL, but can alert an administrator instead (say with an Emailer transformer).