SQL查询选择多个行，其中'field'等于'value'，然后添加与结果关联的其他id

Question

I have a users table that contains persons and their status. The ID field is not unique.

ID | Name | Status
1  | Jon  | Online
2  | Ken  | Away
3  | Kim  | Online
4  | Van  | Offline
1  | Jon  | NULL
2  | Ken  | NULL
3  | Kim  | NULL
4  | Van  | NULL
1  | Jon  | Online

In this case, I want to get the Users that are online and all the other same ids of the user in this table to form like this.

ID | Name | Status
1  | Jon  | Online
1  | Jon  | Online
1  | Jon  | NULL
3  | Kim  | Online
3  | Kim  | NULL

Is there a way to get this result with one select statement?

Answer 1

Without a login timestamp, it doesn't give you much information of how you want to get the most recent event for a person. If they can have 3 rows, how do you know which one means they ARE online and which one means they WERE online.

http://sqlfiddle.com/#!6/3833e/4 <<< MS SQL Setup

http://sqlfiddle.com/#!4/f190f/2 <<< Oracle SQL Setup

The Fiddle gives you the people in descending order of most recent login grouped by person. If you only want to grab the most recent logins, use the second select on the SQL side.

SELECT t1.ID
    , t1.Name
    , t1.Status
    , t1.OnlineTimeStamp
    , ROW_NUMBER() OVER ( PARTITION BY t1.ID ORDER BY t1.OnlineTimeStamp DESC ) AS rn
FROM Test_Client t1
WHERE EXISTS ( SELECT 1 FROM Test_Client t2 WHERE t2.ID = t1.ID AND t2.Status = 'Online' )
ORDER BY t1.ID, rn

;

SELECT tcSub.ID
    , tcSub.Name
    , tcSub.Status
FROM (
    SELECT t1.ID
        , t1.Name
        , t1.Status
        , t1.OnlineTimeStamp
        , ROW_NUMBER() OVER ( PARTITION BY t1.ID ORDER BY t1.OnlineTimeStamp DESC ) AS rn
    FROM Test_Client t1
    WHERE EXISTS ( SELECT 1 FROM Test_Client t2 WHERE t2.ID = t1.ID AND t2.Status = 'Online' )
    ) tcSub
WHERE tcSub.rn = 1
ORDER BY tcSub.ID

Answer 2

There are a couple ways to do this -- one is to use exists :

select id, name, status
from users u
where exists (
    select 1
    from users u2 
    where u.id = u2.id and u2.status = 'Online'
    )

---

Here's a version using in (although I prefer the prior):

select id, name, status
from users
where id in (
    select id
    from users 
    where status = 'Online'
    )