SQL基於其他領域的計數行的表

Question

我有一個表[報名]具有以下字段更新領域：

1）MEMBERID 2）嘗試

我的一些嘗試是空值。

我想企圖場更新爲0的那些行，其中MEMBERID表中的計數爲1

任何幫助表示讚賞。

Answer 1

UPDATE applicants 
SET Attempts = 0 
WHERE MemberID IN 
    (SELECT MemberID FROM applicants GROUP BY MemberID HAVING COUNT(MemberID)=1) 
    AND Attempts IS NULL 

Answer 2

一般的做法是

update applicants set 
    Attempts = 0 
where 
    MemberID in (select t.MemberID from applicants as t group by t.MemberID having count(*) = 1) and 
    Attempts is null -- if you need it 

在SQL Server

，你可以這樣做：

with cte as (
    select *, count(*) over(partition by MemberID) as cnt 
    from applicants 
) 
update cte set 
    Attempts = 0 
where cnt = 1 and Attempts is null