WHERE clause on JOIN query???

[Mincer]

I have this query:

$sql = "
	SELECT unbilled_item.job_number,
	SUM(unbilled_item.amount) AS total_unbilled,
	job.project_manager
	FROM unbilled_item
	LEFT JOIN job ON (unbilled_item.job_number=job.job_number)
	GROUP BY job.project_manager
	ORDER BY total_unbilled DESC
	" ;

Is it possible to add something like:

WHERE user.office = "xxx"

???

I can't work it out.