INSERT INTO campaigns_activities from activity where activity type is "subscriber" and action is "unsubscribe". (This is for a specific campaign ID which makes the join with "email_messages" pointless.)

unsubscribe-activities-to-campaign-activities.sql

INSERT INTO campaigns_activities (
	SELECT
		a.createdAt,
		a.updatedAt,
		a.id,
		e.campaignId
	FROM
		activities a
	LEFT JOIN
		subscribers s ON (s.uuid = a.target)
	LEFT JOIN
		email_messages e ON (e.subscriberId = s.id AND e.`type` = 'bulk')
	WHERE
		a.type = 'subscriber'
	AND
		a.action = 'unsubscribe'
	AND
		e.campaignId = 4
)