只要 reservation_id 最多出现一张唱片 livestream_reservations ，这将适用于您：

select r.*,
       case
         when l.reservation_id is null then 0
         else 1
       end as is_livestream
  from reservations r
       left join livestream_reservations l
              on l.reservation_id = r.reservation_id;

这个 case 依赖于一个事实 livestream_reservations 退货 null 在该表的所有列中。
如果同一行中可能有多行 reservation_id 在 livestream_reservations 表，然后你可以这样做：

with ls_count as (
  select reservation_id, count(*) as count_livestream
    from livestream_reservations
   group by reservation_id
)
select r.*, coalesce(lc.count_livestream, 0) as count_livestream
  from reservations r
       left join ls_count lc on lc.reservation_id = r.reservation_id;

我建议你 exists 使用布尔函数：

select r.*,
       (exists (select 1 from livestream_reservations lr where lr.reservation_id = r. reservation_id)
       ) as is_livestream
from reservations r;

这很有可能比其他解决方案更快。更重要的是，它避免了在 livestream_reservations .