Du angiver ikke dit RDBMS, så her er det i MySQL
DELETE teammembers FROM teammembers
JOIN teams on teammembers.teamId = teams.teamId
WHERE teams.eventId = 1
Du angiver ikke dit RDBMS, så her er det i MySQL
DELETE teammembers FROM teammembers
JOIN teams on teammembers.teamId = teams.teamId
WHERE teams.eventId = 1