MIN date from within GROUP

Question

I'm trying to work out if the following is possible within a single query.

We have the following Query that gets information from Tables A and B

SELECT 
     a.wj_job
     ,a.wj_sched
     ,a.wj_lump
     ,SUM(b.wj_billed) AS wj_billed
     ,SUM(b.wj_received) AS wj_recd
     ,a.wj_lbdate
     ,a.wj_fecom1 
FROM ag_fsch a
     JOIN ag_fschd b ON a.wj_job = b.wj_jbnum AND a.wj_sched = b.wj_sched 
WHERE 
     a.wj_job LIKE "4733.%"
GROUP BY 
     a.wj_job
     ,a.wj_sched 
ORDER BY 
     a.wj_job
     ,a.wj_sched

I would like to extract the last unpaid bill date from table b as part of the above Query. The same thing can be achieved by the query below, but only for a specific result in the original Query.

SELECT 
     MIN(wj_bdate) 
FROM ag_fschd
WHERE 
     wj_jbnum = 4733.00
     AND wj_sched = 6
     AND wj_billed <> 0
     AND wj_received = 0

Answer 1

I think you can use conditional aggregation. I'm not sure because there are two keys in the group by , not just the job number. But, this may be the output you want:

SELECT a.wj_job, a.wj_sched, a.wj_lump, SUM(b.wj_billed) AS wj_billed,
       SUM(b.wj_received) AS wj_recd, a.wj_lbdate, a.wj_fecom1,
       MIN(CASE WHEN b.wj_sched = 6 AND b.wj_billed <> 0 AND b.wj_received = 0
                THEN wj_bdate
           END)
FROM ag_fsch a JOIN
     ag_fschd b
     ON a.wj_jbnum = b.wj_jbnum AND a.wj_sched = b.wj_sched 
WHERE a.wj_jbnum LIKE '4733.%'
GROUP BY a.wj_jbnum, a.wj_sched 
ORDER BY a.wj_jbnum, a.wj_sched;

Answer 2

Using a sub query to get the min date for each one:-

SELECT a.wj_job, 
        a.wj_sched, 
        a.wj_lump, 
        SUM(b.wj_billed) AS wj_billed,
        SUM(b.wj_received) AS wj_recd, 
        a.wj_lbdate, 
        a.wj_fecom1 ,
        sub0.wj_bdate
FROM ag_fsch a
JOIN ag_fschd b ON a.wj_jbnum = b.wj_jbnum AND a.wj_sched = b.wj_sched 
LEFT OUTER JOIN
(
    SELECT wj_jbnum,
            wj_sched,
            MIN(wj_bdate) 
    FROM ag_fschd
    WHERE wj_billed <> 0
    AND wj_received = 0
    GROUP BY wj_jbnum,
            wj_sched
) sub0
ON sub0.wj_jbnum = a.wj_jbnum AND sub0.wj_sched = a.wj_sched
WHERE a.wj_jbnum LIKE "4733.%"
GROUP BY a.wj_jbnum, a.wj_sched 
ORDER BY a.wj_jbnum, a.wj_sched

Note as Jarlh pointed out in the comments, the GROUP BY clause is a bit odd as it doesn't have all the non aggregate fields in it. I have made no attempt to fix that here.