如何检查具有相同外键的记录是否具有某些值

Question

See below table:

id foreign_key_id event_type event_status
---------------------------------------
1        1            20         1
2        1            20         2
3        1            30         1
4        1            30         2
5        2            20         1
6        2            20         2
7        2            30         1

Basically, I want to a query to return only foreign keys which have a record with event type 20 with status 1 but don't have a record with event type 30 and status 2

In this scenario it should return the fk 2.

Answer 1

You can use a correlated subquery.

SELECT DISTINCT foreign_key_id
FROM yourTable AS t1
WHERE t1.event_type = 20 and t1.event_status = 1
AND foreign_key_id NOT IN (
    SELECT foreign_key_id
    FROM yourTable AS t2
    WHERE t1.foreign_key_id = t2.foreign_key_id
    AND t2.event_type = 30 AND t2.event_status = 2)

DEMO

It can also be done with a LEFT JOIN :

SELECT DISTINCT t1.foreign_key_id
FROM yourTable AS t1
LEFT JOIN yourTable AS t2
ON t1.foreign_key_id = t2.foreign_key_id
    AND t2.event_type = 30 AND t2.event_status = 2
WHERE t1.event_type = 20 and t1.event_status = 1
AND t2.id IS NULL

DEMO

Answer 2

select distinct foreign_key_id 
from tablename
where event_type = 20 
and event_status = 1 
and foreign_key_id not in (
    select distinct foreign_key_id 
    from tablename 
    where event_type = 30 
    and event_status = 2
);

Hope it helps.