只选择重复

Question

最上面是一个示例数据库。我需要查询来显示

1. 过滤一次进行多个项目的客户。
2. 删除当前没有正在进行项目的客户的记录（过去项目的记录应该删除）。

请帮

GROUP BY CustomerID 
Having COUNT(*) >= 1 is not working 

Answer 1

对于重复出现是不同的工艺，例如，你可以使用窗口函数：

;with cte as (
    select *, count(*) over(partition by customerID) as cnt 
    from <Table> 
) 
select * 
from cte 
where 
    cnt > 1 

Answer 2

，仅保留最近的项目，使用row_number()：

with t as (
    select t.*, 
      row_number() over (partition by customerid order by enddate desc) as seqnum 
    from table t 
    ) 
select t.* 
from t 
where seqnum > 1; 

致力于LLY从数据库中删除旧的记录，你可以使用一个类似的结构：

with todelete as (
    select t.*, 
      row_number() over (partition by customerid order by enddate desc) as seqnum 
    from table t 
    ) 
delete from todelete 
where seqnum = 1; 

不过，如果你只是想在客户没有正在进行proejct：

select customerid 
from table t 
group by customerid 
having sum(case when getdate() between startdate and endate then 1 else 0 end) = 0;