Question

Sorry for a long question and not a very descriptive title, but my problem is very difficult to explain briefly.

I have three database tables:

TABLE A:  
AID PK  
STATUS VARCHAR

TABLE B:  
BID PK  
AID FK  
CID FK

TABLE C:  
CID PK  
CREATIONTIME DATE

For each STATUS = ‘OK’ row in table A I want to find the corresponding row in C which has the latest creation time.

First I can to fetch all rows from table A where STATUS = ‘OK’.
Next I can to fetch all corresponding rows from table B.
But how to continue from there?

For example:

select AID, CID from B where AID in (select AID from A where STATUS = 'OK')

could return something like:

AID, CID  
1    1  
2    2  
2    3  
3    4  
4    5  
4    6  

Let’s say that CID 2 has later creation time than CID 3 and CID 6 is newer than CID 5. This means that the correct result would be rows 1, 2, 4 and 6 in table C.

Is there a way to express this with a query?

EDIT:
Sorry that I wasn’t specific enough. What I want to get is the CIDs from table C.

EDIT:
I counted returned rows with the different solutions. Results were very interesting – and diversified:
HAINSTECH: 298 473 rows
JMUCCHIELLO: 298 473 rows
RUSS CAM: 290 121 rows
CHRIS: 344 093 rows
TYRANNOSAURS: 290 119 rows

I have not yet had the time to analyse returned rows in depth, but I’d really appreciate views on which of the queries are “broken” and why.

Answer 1

Something like this, if I’ve understood you correctly

SELECT
    MAX(CREATIONTIME),
    A.AID
FROM
    A
INNER JOIN
    B
    ON 
    A.AID = B.AID
INNER JOIN
    C
    ON 
    B.CID = C.CID
WHERE
    A.STATUS = 'OK'
GROUP BY
    A.AID

EDIT:

I have now checked the following in SQL Server (I would epxect the same outcome in Oracle) and it returns the CID for the C record with the Maximum CREATIONTIME where the STATUS for the related record in A id 'OK'.

SELECT C.CID
FROM 
C C
INNER JOIN
B B
ON 
C.CID = B.CID
INNER JOIN
(
    SELECT
        MAX(C.CREATIONTIME) CREATIONTIME,
        A.AID
    FROM
        A A
    INNER JOIN
        B B
        ON 
        A.AID = B.AID
    INNER JOIN
        C C
        ON 
        B.CID = C.CID
    WHERE
        A.STATUS = 'OK'
    GROUP BY
        A.AID
) ABC
ON B.AID = ABC.AID
AND C.CREATIONTIME = ABC.CREATIONTIME

Demonstrated with the following T-SQL

DECLARE @A TABLE(AID INT IDENTITY(1,1), STATUS VARCHAR(10))
DECLARE @B TABLE(BID INT IDENTITY(1,1), AID INT, CID INT)
DECLARE @C TABLE(CID INT IDENTITY(1,1), CREATIONTIME DATETIME)

INSERT INTO @A VALUES ('OK')
INSERT INTO @A VALUES ('OK')
INSERT INTO @A VALUES ('NOT OK')
INSERT INTO @A VALUES ('OK')
INSERT INTO @A VALUES ('NOT OK')

INSERT INTO @C VALUES ('10 MAR 2008')
INSERT INTO @C VALUES ('13 MAR 2008')
INSERT INTO @C VALUES ('15 MAR 2008')
INSERT INTO @C VALUES ('17 MAR 2008')
INSERT INTO @C VALUES ('21 MAR 2008')

INSERT INTO @B VALUES (1,1)
INSERT INTO @B VALUES (1,2)
INSERT INTO @B VALUES (1,3)
INSERT INTO @B VALUES (2,2)
INSERT INTO @B VALUES (2,3)
INSERT INTO @B VALUES (2,4)
INSERT INTO @B VALUES (3,3)
INSERT INTO @B VALUES (3,4)
INSERT INTO @B VALUES (3,5)
INSERT INTO @B VALUES (4,5)
INSERT INTO @B VALUES (4,1)
INSERT INTO @B VALUES (4,2)


SELECT C.CID
FROM 
@C C
INNER JOIN
@B B
ON 
C.CID = B.CID
INNER JOIN
(
SELECT
    MAX(C.CREATIONTIME) CREATIONTIME,
    A.AID
FROM
    @A A
INNER JOIN
    @B B
    ON 
    A.AID = B.AID
INNER JOIN
    @C C
    ON 
    B.CID = C.CID
WHERE
    A.STATUS = 'OK'
GROUP BY
    A.AID
) ABC
ON B.AID = ABC.AID
AND C.CREATIONTIME = ABC.CREATIONTIME

Results in the following

CID
-----------
3
4
5

EDIT 2:

In response to your comment about each of the statements giving different results, I have ran some of the different answers here through SQL Server 2005 using my test data above (I appreciate you are using Oracle). Here are the results

--Expected results for CIDs would be

--CID
-----------
--3
--4
--5

--As indicated in the comments next to the insert statements

DECLARE @A TABLE(AID INT IDENTITY(1,1), STATUS VARCHAR(10))
DECLARE @B TABLE(BID INT IDENTITY(1,1), AID INT, CID INT)
DECLARE @C TABLE(CID INT IDENTITY(1,1), CREATIONTIME DATETIME)

INSERT INTO @A VALUES ('OK') -- AID 1
INSERT INTO @A VALUES ('OK') -- AID 2
INSERT INTO @A VALUES ('NOT OK')
INSERT INTO @A VALUES ('OK') -- AID 4
INSERT INTO @A VALUES ('NOT OK')

INSERT INTO @C VALUES ('10 MAR 2008')
INSERT INTO @C VALUES ('13 MAR 2008')
INSERT INTO @C VALUES ('15 MAR 2008')
INSERT INTO @C VALUES ('17 MAR 2008')
INSERT INTO @C VALUES ('21 MAR 2008')

INSERT INTO @B VALUES (1,1)
INSERT INTO @B VALUES (1,2)
INSERT INTO @B VALUES (1,3) -- Will be CID 3 For AID 1
INSERT INTO @B VALUES (2,2)
INSERT INTO @B VALUES (2,3)
INSERT INTO @B VALUES (2,4) -- Will be CID 4 For AID 2
INSERT INTO @B VALUES (3,3)
INSERT INTO @B VALUES (3,4)
INSERT INTO @B VALUES (3,5)
INSERT INTO @B VALUES (4,5) -- Will be CID 5 FOR AID 4
INSERT INTO @B VALUES (4,1)
INSERT INTO @B VALUES (4,2)

-- Russ Cam
SELECT C.CID, ABC.CREATIONTIME
FROM 
@C C
INNER JOIN
@B B
ON 
C.CID = B.CID
INNER JOIN
(
SELECT
    MAX(C.CREATIONTIME) CREATIONTIME,
    A.AID
FROM
    @A A
INNER JOIN
    @B B
    ON 
    A.AID = B.AID
INNER JOIN
    @C C
    ON 
    B.CID = C.CID
WHERE
    A.STATUS = 'OK'
GROUP BY
    A.AID
) ABC
ON B.AID = ABC.AID
AND C.CREATIONTIME = ABC.CREATIONTIME

-- Tyrannosaurs
select   A.AID,  
         max(AggC.CREATIONTIME)  
from    @A A,  
         @B B,  
         (  select  C.CID,  
             max(C.CREATIONTIME) CREATIONTIME  
            from @C C  
            group by CID
          ) AggC  
where    A.AID = B.AID  
and    B.CID = AggC.CID  
and    A.Status = 'OK'  
group by A.AID

-- jmucchiello
SELECT c.cid, max(c.creationtime)
FROM @B b, @C c
WHERE b.cid = c.cid
 AND b.aid IN (SELECT a.aid FROM @A a WHERE status = 'OK')
GROUP BY c.cid

-- hainstech
SELECT agg.aid, agg.cid
FROM (
    SELECT a.aid
        ,c.cid
        ,max(c.creationtime) as maxcCreationTime
    FROM @C c INNER JOIN @B b ON b.cid = c.cid
        INNER JOIN @A a on a.aid = b.aid
    WHERE a.status = 'OK'
    GROUP BY a.aid, c.cid
) as agg

--chris
SELECT A.AID, C.CID, C.CREATIONTIME
FROM @A A, @B B, @C C
WHERE A.STATUS = 'OK'
AND A.AID = B.AID
AND B.CID = C.CID
AND C.CREATIONTIME = 
(SELECT MAX(C2.CREATIONTIME) 
FROM @C C2, @B B2 
WHERE B2.AID = A.AID
AND C2.CID = B2.CID);

the results are as follows

--Russ Cam - Correct CIDs (I have added in the CREATIONTIME for reference)
CID         CREATIONTIME
----------- -----------------------
3           2008-03-15 00:00:00.000
4           2008-03-17 00:00:00.000
5           2008-03-21 00:00:00.000

--Tyrannosaurs - No CIDs in the resultset
AID         
----------- -----------------------
1           2008-03-15 00:00:00.000
2           2008-03-17 00:00:00.000
4           2008-03-21 00:00:00.000


--jmucchiello - Incorrect CIDs in the resultset
cid         
----------- -----------------------
1           2008-03-10 00:00:00.000
2           2008-03-13 00:00:00.000
3           2008-03-15 00:00:00.000
4           2008-03-17 00:00:00.000
5           2008-03-21 00:00:00.000

--hainstech - Too many CIDs in the resultset, which CID has the MAX(CREATIONTIME) for each AID?
aid         cid
----------- -----------
1           1
1           2
1           3
2           2
2           3
2           4
4           1
4           2
4           5

--chris - Correct CIDs, it is the same SQL as mine
AID         CID         CREATIONTIME
----------- ----------- -----------------------
1           3           2008-03-15 00:00:00.000
2           4           2008-03-17 00:00:00.000
4           5           2008-03-21 00:00:00.000

I would recommend running each of the given answers against a smaller number of records, so that you can ascertain whether the resultset returned is the expected one.