Oracle: select just last update of date - sql

Question

I have the following query that return me: 100 rows
SELECT uni_id, uni_mast_id, uni_type
FROM UNIVERSITIES
WHERE uni_master ='SO88'AND uni_stat= 'OK'
now i need to do a join with another table and to obtain last entry of that day then:
SELECT uni_id, uni_teach_name, MAX(cal_update), cal_status
FROM UNIVERSITIES
LEFT JOIN CALENDAR
ON unı_id = cal_id
WHERE uni_master = 'SO88'
AND uni_stat = 'OK'
AND cal_name = 'REGISTRED'
GROUP BY uni_id, uni_teach_name, uni_stat
ORDER BY cal_update
but this query gives me 102 records, because cal_update appears 2 times.
One for example with date : 22-OCT-2020 11:34:55 another for the same uni_id at time 22-OCT-2020 11:30:22
I want just to get the max date for that date, not both.
In this case the query with the join needs to return the same records of the first select query.

Answer 1

I think you can do what you want using row_number():
SELECT UNI_ID, UNI_TEACH_NAME, CAL_UPDATE, CAL_STATUS
FROM (SELECT U.UNI_ID, U.UNI_TEACH_NAME, C.CAL_UPDATE, C.CAL_STATUS,
ROW_NUMBER() OVER (PARTITION BY U.UNI_ID, TRUNC(C.CAL_UPDATE) ORDER BY C.CAL_UPDATE DESC) as seqnum
FROM UNIVERSITIES U LEFT JOIN
CALENDAR C
ON U.UNI_ID = C.CAL_ID AND C.CAL_NAME = 'REGISTRED'
WHERE U.UNI_MASTER = 'SO88' AND
U.UNI_STAT= 'OK'
) UC
WHERE seqnum = 1;
I have to guess where the columns come from, because the question is not clear. Any filtering columns from CALENDAR should be in the ON clause if you are using a LEFT JOIN.

Answer 2

You can replace the last part of the query, while aliasing the MAX(cal_update) with cal_update , as
ORDER BY cal_update DESC
FETCH FIRST 1 ROW WITH TIES
for DB version 12c+ to descendingly order by the concerned column in order to pick the record with the latest value for that column.
WITH TIES option stand for bringing all records with the same datetime values, might be replaced with ONLY in order to bring only one row even for those cases occur.
The column call_status(within the select list) should be removed which's a non- aggregated column

Answer 3

As an alternative to a subquery and rank, you could use KEEP...LAST :
SELECT U.UNI_ID,
U.UNI_TEACH_NAME,
MAX(C.CAL_UPDATE) AS CAL_UPDATE,
MAX(C.CAL_STATUS) KEEP (DENSE_RANK LAST ORDER BY C.CAL_UPDATE) AS CAL_STATUS
FROM UNIVERSITIES U
LEFT JOIN CALENDAR C
ON U.UNI_ID = C.CAL_ID
AND C.CAL_NAME = 'REGISTRED'
WHERE U.UNI_MASTER = 'SO88'
AND U.UNI_STAT= 'OK'
GROUP BY U.UNI_ID,
U.UNI_TEACH_NAME,
TRUNC(C.CAL_UPDATE)
I've moved the CAL_NAME check into the outer join's ON clause; if it's in the WHERE clause then it will effectively turn it back into an inner join. So this will get one row per university per day that the calendar was updated: "I want just to get the max date for that date". And it will show nulls for the calendar fields if there is no matching calendar, since it's an outer join.
If you actually only want the latest update on any day then just remove the TRUNC(C.CAL_UPDATE) from the grouping:
SELECT U.UNI_ID,
U.UNI_TEACH_NAME,
MAX(C.CAL_UPDATE) AS CAL_UPDATE,
MAX(C.CAL_STATUS) KEEP (DENSE_RANK LAST ORDER BY C.CAL_UPDATE) AS CAL_STATUS
FROM UNIVERSITIES U
LEFT JOIN CALENDAR C
ON U.UNI_ID = C.CAL_ID
AND C.CAL_NAME = 'REGISTRED'
WHERE U.UNI_MASTER = 'SO88'
AND U.UNI_STAT= 'OK'
GROUP BY U.UNI_ID,
U.UNI_TEACH_NAME
db<>fiddle with some made-up data; and also (just for fun) showing Gordon's query with the calendar name clause in both places to show the difference, and to show this gets the same result for that dummy data. (And an 18c version which shows Barbaros' too; getting back a single row.)