mysql update query with sub query

Question

Can anyone see what is wrong with the below query?

When I run it I get:

#1064 - You have an error in your SQL syntax; check the manual that co

Answer 1

For the impatient:

UPDATE target AS t
INNER JOIN (
  SELECT s.id, COUNT(*) AS count
  FROM source_grouped AS s
  -- WHERE s.custom_condition IS (true)
  GROUP BY s.id
) AS aggregate ON aggregate.id = t.id
SET t.count = aggregate.count

That's @mellamokb's answer, as above, reduced to the max.