只選擇重複

Question

最上面是一個示例數據庫。我需要查詢來顯示

1. 過濾一次進行多個項目的客戶。
2. 刪除當前沒有正在進行項目的客戶的記錄（過去項目的記錄應該刪除）。

請幫

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

Answer 1

對於重複出現是不同的工藝，例如，你可以使用窗口函數：

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

Answer 2

，僅保留最近的項目，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; 

致力於LLY從數據庫中刪除舊的記錄，你可以使用一個類似的結構：

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; 

不過，如果你只是想在客戶沒有正在進行proejct：

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