连接

• 570. 至少有5名直接下属的经理 - 力扣（LeetCode）

select Employee.Name as Name
from (
  select ManagerId as Id
  from Employee
  group by ManagerId
  having count(Id) >= 5
) as Manager join Employee
on Manager.Id = Employee.Id

• 1934. 确认率 - 力扣（LeetCode）

select a.user_id,
round(sum(if (b.action='confirmed',1.00,0.00)) / count(a.user_id), 2) as confirmation_rate 
from Signups a left join Confirmations b on a.user_id = b. user_id
group by a.user_id