Subquery return more than one value - sql

Question

I have the following query which gives gives req_no and order_no. order_no is a from a sub_query which you can see from below sql. For a few req_no there are more than one order_no's and because of that I get ORA-01427: single-row subquery returns more than one row.
I would like to display both the order_no for one req_no, how can I achieve this?
Any help is highly appreciable.
Thanks
P.S. Our client's one database is still Oracle 8i.
SELECT max_qst.req_no,
(SELECT DISTINCT max_odr.order_no
FROM maximo_orders max_odr,
maximo_order_revisions max_odv,
maximo_order_items max_odi,
maximo_order_dates max_odd,
maximo_requisition_order max_rqo,
maximo_requisition_details max_req
WHERE max_req.req_no = max_qst.req_no
AND max_req.req_yr = max_qst.req_yr
AND max_odr.order_no = max_odi.order_no
AND max_odi.order_item_id = max_odd.order_item_id
AND max_req.requisition_item_id = max_rqo.requisition_item_id
AND max_rqo.order_schedule_id = max_odd.order_schedule_id
AND max_odv.order_no = max_odi.order_no
AND max_odv.revision_no =
(SELECT MAX (max_alias.revision_no)
FROM maximo_order_revisions max_alias
WHERE max_alias.order_no = max_odv.order_no)
AND maximo_order_item (max_odi.order_no,
max_odv.revision_no,
max_odi.order_item_id
) = 'CONFIRMED'
)
FROM maximo_requisitions max_qst, maximo_requisition_details max_qsd
WHERE max_qst.qst_id = max_qsd.qst_id
AND max_qst.enter_date = '2001'
AND max_qst.req_no = 'PUR_12WX'
Update 1
Desired out put.
REQ_No ORDER_NO
PUR_12WX PR_9078
PUR_12WX PR_9079

Answer 1

Use a join instead of a correlated sub-query.
I've removed the max_qst references from the sub-query and moved them to the join predicate.
I've also just changed it to use a LEFT JOIN. This allows for the possibility of there being no order_no values returned.
SELECT
max_qst.req_no,
sub_query.order_no
FROM
maximo_requisitions max_qst
INNER JOIN
maximo_requisition_details max_qsd
ON max_qst.qst_id = max_qsd.qst_id
LEFT JOIN
(
SELECT DISTINCT
max_odr.order_no,
max_req.req_no,
max_req.req_yr
FROM
maximo_orders max_odr,
maximo_order_revisions max_odv,
maximo_order_items max_odi,
maximo_order_dates max_odd,
maximo_requisition_order max_rqo,
maximo_requisition_details max_req
WHERE
max_odr.order_no = max_odi.order_no
AND max_odi.order_item_id = max_odd.order_item_id
AND max_req.requisition_item_id = max_rqo.requisition_item_id
AND max_rqo.order_schedule_id = max_odd.order_schedule_id
AND max_odv.order_no = max_odi.order_no
AND max_odv.revision_no = (SELECT MAX (max_alias.revision_no)
FROM maximo_order_revisions max_alias
WHERE max_alias.order_no = max_odv.order_no)
AND maximo_order_item (max_odi.order_no, max_odv.revision_no, max_odi.order_item_id) = 'CONFIRMED'
)
suq_query
ON max_qst.req_no = sub_query.req_no
AND max_qst.req_yr = sub_query.req_yr
WHERE
max_qst.enter_date = '2001'
max_qst.req_no = 'PUR_12WX'

Answer 2

You can use
DISTINCT
or
WHERE ROWNUM = 1
But I'd suggest you investigate why you're getting more than one row returned: Have you misunderstood the data, have you missed a join, is there erroneous or duplicate data etc etc.