sql update from sub-query

update-from-sub-query.sql

-- great way to batch update using a sub-query in the from clause
update category set catid=100
from (
   select event.catid
   from event
   left join category cat on event.catid = cat.catid
   where cat.catid is null
   limit 1000
) eventcat
where category.catid = eventcat.catid
and catgroup='Concerts';