Performance tuning of Oracle SQL query - sql

Question

Can someone help me out to tune this query? It's taking 1 minute time to return the data in sqldeveloper.
SELECT
masterid, notification_id, notification_list, typeid,
subject, created_at, created_by, approver, sequence_no,
productid, statusid, updated_by, updated_at, product_list,
notification_status, template, notification_type, classification
FROM
(
SELECT
masterid, notification_id, notification_list, typeid, subject,
approver, created_at, created_by, sequence_no, productid,
statusid, updated_by, updated_at, product_list, notification_status,
template, notification_type, classification,
ROW_NUMBER() OVER(ORDER BY masterid DESC)AS r
FROM
(
SELECT DISTINCT
a.masterid AS masterid,
a.maxid AS notification_id,
notification_list,
typeid,
noti.subject AS subject,
noti.approver AS approver,
noti.created_at AS created_at,
noti.created_by AS created_by,
noti.sequence_no AS sequence_no,
a.productid AS productid,
a.statusid AS statusid,
noti.updated_by AS updated_by,
noti.updated_at AS updated_at,
(
SELECT LISTAGG(p.name,',') WITHIN GROUP(ORDER BY p.id) AS list_noti
FROM product p
INNER JOIN notification_product np ON np.product_id = p.id
WHERE notification_id = a.maxid
) AS product_list,
(
SELECT description
FROM notification_status
WHERE id = a.statusid
) AS notification_status,
(
SELECT name
FROM template
WHERE id = a.templateid
) AS template,
(
SELECT description
FROM notification_type
WHERE id = a.typeid
) AS notification_type,
(
SELECT tc.description
FROM template_classification tc
INNER JOIN notification nt ON tc.id = nt.classification_id
WHERE nt.id = a.maxid
) AS classification
FROM
(
SELECT
nm.id AS masterid,
nm.product_id AS productid,
nm.notification_status_id AS statusid,
nm.template_id AS templateid,
nm.notification_type_id AS typeid,
(
SELECT MAX(id)
FROM notification
WHERE notification_master_id = nm.id
) AS maxid,
(
SELECT LISTAGG(n.id,',') WITHIN GROUP(ORDER BY nf.id) AS list_noti
FROM notification n
WHERE notification_master_id = nm.id
) AS notification_list
FROM notification_master nm
INNER JOIN notification nf ON nm.id = nf.notification_master_id
WHERE nm.disable = 'N'
ORDER BY nm.id DESC
) a
INNER JOIN notification noti
ON a.maxid = noti.id
AND
(
(
(
TO_DATE('01-jan-1970','dd-MM-YYYY') +
numtodsinterval(created_at / 1000,'SECOND')
) <
(current_date + INTERVAL '-21' DAY)
)
OR (typeid exists(2,4) AND statusid = 4)
)
)
)
WHERE r BETWEEN 11 AND 20

Answer 1

DISTINCT is very often an indicator for a badly written query. A normalized database doesn't contain duplicate data, so where do the duplicates suddenly come from that you must remove with DISTINCT? Very often it is your own query producing these. Avoid producing duplicates in the first place, so you don't need DISTINCT later.
In your case you are joining with the table notification in your subquery a, but you are not using its rows in that subquery; you only select from notification_master_id.
After all, you want to get notification masters, get their latest related notification (by getting its ID first and then select the row). You don't need hundreds of subqueries to achieve this.
Some side notes:
To get the description from template_classification you are joining again with the notification table, which is not necessary.
ORDER BY in a subquery (ORDER BY nm.id DESC) is superfluous, because subquery results are per standard SQL unsorted. (Oracle violates this standard sometimes in order to apply ROWNUM on the result, but you are not using ROWNUM in your query.)
It's a pity that you store created_at not as a DATE or TIMESTAMP, but as a number. This forces you to calculate. I don't think this has a great impact on your query, though, because you are using it in an OR condition.
CURRENT_DATE gets you the client date. This is rarely wanted, as you select data from the database, which should of course not relate to some client's date, but to its own date SYSDATE.
If I am not mistaken, your query can be shortened to:
SELECT
nm.id AS masterid,
nf.id AS notification_id,
nfagg.notification_list AS notification_list,
nm.notification_type_id AS typeid,
nf.subject AS subject,
nf.approver AS approver,
nf.created_at AS created_at,
nf.created_by AS created_by,
nf.sequence_no AS sequence_no,
nm.product_id AS productid,
nm.notification_status_id AS statusid,
nf.updated_by AS updated_by,
nf.updated_at AS updated_at,
(
SELECT LISTAGG(p.name, ',') WITHIN GROUP (ORDER BY p.id)
FROM product p
INNER JOIN notification_product np ON np.product_id = p.id
WHERE np.notification_id = nf.id
) AS product_list,
(
SELECT description
FROM notification_status
WHERE id = nm.notification_status_id
) AS notification_status,
(
SELECT name
FROM template
WHERE id = nm.template_id
) AS template,
(
SELECT description
FROM notification_type
WHERE id = nm.notification_type_id
) AS notification_type,
(
SELECT description
FROM template_classification
WHERE id = nf.classification_id
) AS classification
FROM notification_master nm
INNER JOIN
(
SELECT
notification_master_id,
MAX(id) AS maxid,
LISTAGG(id,',') WITHIN GROUP (ORDER BY id) AS notification_list
FROM notification
GROUP BY notification_master_id
) nfagg ON nfagg.notification_master_id = nm.id
INNER JOIN notification nf
ON nf.id = nfagg.maxid
AND
(
(
DATE '1970-01-01' + NUMTODSINTERVAL(nf.created_at / 1000, 'SECOND')
< CURRENT_DATE + INTERVAL '-21' DAY
)
OR (nm.notification_type_id IN (2,4) AND nm.notification_status_id = 4)
)
WHERE nm.disable = 'N'
ORDER BY nm.id DESC
OFFSET 10 ROWS
FETCH NEXT 10 ROWS ONLY;
As mentioned, you may want to replace CURRENT_DATE with SYSDATE.
I recommend the following indexes for the query:
CREATE INDEX idx1 ON notification_master (disable, id, notification_status_id, notification_type_id);
CREATE INDEX idx2 ON notification (notification_master_id, id, created_at);
A last remark on paging: In order to skip n rows to get the next n, the whole query must get executed for all data and then all result rows be sorted only to pick n of them at last. It is usually better to remember the last fetched ID and then only select rows with a higher ID in the next execution.