Are there way/s for me to extract data that only contain a certain values in sql? - sql

Question

Are there way/s for me to extract data that only contain a certain values.
Ex:
Contact Asset Status
AB 1 Cancelled
AB 2 Cancelled
AB 3 Cancelled
AB 4 Cancelled
CD 5 Cancelled
CD 6 Active
CD 7 Cancelled
CD 8 Active
What I want to get are only those contacts that does contain cancelled assets ONLY (like Contact AB). And not those with both cancelled and active assets (like Contact CD).

Answer 1

You can do this with group by and a having clause:
select contact
from table t
group by contact
having min(status) = 'Cancelled' and max(status) = 'Cancelled';
This works for the data in your example. If status could be NULL and you want to count that as a different value, then the logic would be slightly more complicated.

Answer 2

The pure relational logic way is easier to understand, but will perform less well, requiring some kind of join to work. Let's satisfy the conditions
There is at least one status Cancelled for each Contact
But there are 0 statuses for that same Contact that aren't Cancelled
in a query like so:
SELECT DISTINCT
CS.Contact
FROM
ContactStatus CS
WHERE
CS.Status = 'Cancelled' -- at least one cancelled
AND NOT EXISTS ( -- but there are none of...
SELECT *
FROM ContactStatus CS2 -- contacts in the same table
WHERE
CS.Contact = CS2.Contact -- for that same contact
AND CS.Status <> 'Cancelled' -- that aren't cancelled
)
;
But we can do this with an aggregate, that will take only a single scan of the table, by using a little thought:
SELECT
Contact
FROM
ContactStatus
GROUP BY
Contact
HAVING
Count(*) = Count(CASE WHEN Status = 'Cancelled' THEN 1 END)
;
Other aggregate expressions in the HAVING clause are possible, such as:
Count(CASE WHEN Status <> 'Cancelled' THEN 1 END) = 0 -- or Min()
Min(Status) = 'Cancelled' AND Max(Status) = 'Cancelled'
Max(CASE WHEN Status = 'Cancelled' THEN 0 ELSE 1 END) = 0
Sum(SELECT 1 WHERE Status <> 'Cancelled') = 0
All of these would do the trick in this case; pick the one that makes the most sense to you.

Answer 3

Select contact from contacts a
where a.status = 'Canceled' AND contact = 'AB'