Postgresql嵌套聚合函数

我想找到当月休假次数最多的员工

我从以下问题开始：

select MAX(TotalLeaves) as HighestLeaves 
FROM (SELECT emp_id, count(adate) as TotalLeaves 
      from attendance 
      group by emp_id) AS HIGHEST;

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但是我在显示员工id和仅获取当月结果方面遇到了问题。请帮助我。

如果您只想在当前查询中显示相应的员工id，您可以对结果进行排序并获得前1行，并且您需要在组之前筛选数据以仅获得当前月份：

select
    emp_id, TotalLeaves
from (
    select emp_id, count(adate) as TotalLeaves 
    from attendance
    where adate >= date_trunc('month', current_date)
    group by emp_id
) as highest
order by TotalLeaves desc
limit 1;

实际上，这里根本不需要使用子查询：

select emp_id, count(adate) as TotalLeaves 
from attendance
where adate >= date_trunc('month', current_date)
group by emp_id
order by TotalLeaves desc
limit 1;

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谢谢您的回答。这真的很有帮助。我还有另一个问题。我有两个表：销售（发票id、客户id、销售日期、总金额）和发票（发票id、数量、价格、产品id、总金额）。我怎样才能找到上周没有售出的产品？？？@user2944346我想最好再问一个问题

SELECT emp_id, count(adate) as TotalLeaves 
  from attendance
  where adata > date_trunc('month', NOW())
  group by emp_id
  order by 2 desc limit 1