SQL基于其他领域的计数行的表

Question

我有一个表[报名]具有以下字段更新领域：

1）MEMBERID 2）尝试

我的一些尝试是空值。

我想企图场更新为0的那些行，其中MEMBERID表中的计数为1

任何帮助表示赞赏。

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

，你可以这样做：

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