Subquery SQL DB2 - sql

Question

I am trying to create a subquery (for a particular column) inside my base query. the code is as follows.
SELECT z.po_id,
max
(
select etcdc.ship_evnt_tms
FROM covinfos.shipment_event etcdc
WHERE etcdc.ship_evnt_cd = '9P'
AND etcdc.ship_id=scdc.ship_id
ORDER BY etcdc.updt_job_tms desc
FETCH first ROW only) AS llp_estimated_delivery_cdc
FROM covinfos.ibm_plant_order z
LEFT JOIN covinfos.ipo_line_to_case a
ON z.po_id = a.po_id
LEFT JOIN covinfos.shipment scdc
ON (
a.ship_id = scdc.ship_id
AND a.ship_to_loc_code = scdc.ship_to_loc_code
AND scdc.loc_type = 'CDC')
GROUP BY z.po_id
There seems to be some kind of typo somewhere based on the error message that pops up when I try to run the code.
BIC00004. DAL01008. An error occurred while accessing the database.
ILLEGAL SYMBOL ".". SOME SYMBOLS THAT MIGHT BE LEGAL ARE: , ). SQLCODE=-104,
SQLSTATE=42601, DRIVER=3.62.56; THE CURSOR SQL_CURLH200C1 IS NOT IN A
PREPARED STATE. SQLCODE=-514, SQLSTATE=26501, DRIVER=3.62.56
However, at plain sight or at least my sight, there is nothing that spots the misstake. Furthermore, running the subselect in a blank sheet (outside the base query, new one) it does correctly.
Thanks

Answer 1

You would probably be best to remove the co-related sub-select, and just join to a plain sub-select. E.g.
SELECT z.po_id,
max(ship_evnt_tms) AS llp_estimated_delivery_cdc
FROM covinfos.ibm_plant_order z
LEFT JOIN covinfos.ipo_line_to_case a
ON z.po_id = a.po_id
LEFT JOIN covinfos.shipment scdc
ON a.ship_id = scdc.ship_id
AND a.ship_to_loc_code = scdc.ship_to_loc_code
AND scdc.loc_type = 'CDC'
LEFT JOIN
( select ship_id
, ship_evnt_tms
FROM
( select ship_id
, ship_evnt_tms
, row_number() over(partition by ship_id order by updt_job_tms desc) as RN
FROM covinfos.shipment_event
WHERE ship_evnt_cd = '9P'
) s
WHERE RN = 1
) AS etcdc
ON etcdc.ship_id=scdc.ship_id
GROUP BY z.po_id
P.S. you could just INNER JOINs unless you want to include po_id's with no ship_evnt_tms

Answer 2

Try adding parentheses around the sub-select. At least this then parses Data Studio using z/OS validation
SELECT z.po_id,
max
((
select etcdc.ship_evnt_tms
FROM covinfos.shipment_event etcdc
WHERE etcdc.ship_evnt_cd = '9P'
AND etcdc.ship_id=scdc.ship_id
ORDER BY etcdc.updt_job_tms desc
FETCH first ROW only)) AS llp_estimated_delivery_cdc
FROM covinfos.ibm_plant_order z
LEFT JOIN covinfos.ipo_line_to_case a
ON z.po_id = a.po_id
LEFT JOIN covinfos.shipment scdc
ON (
a.ship_id = scdc.ship_id
AND a.ship_to_loc_code = scdc.ship_to_loc_code
AND scdc.loc_type = 'CDC')
GROUP BY z.po_id
Still, I'm not sure this is a very nice bit of SQL code.