select single row based on count of rows present oracle - sql

Question

I've got below table using a query, Now I want to fetch single record based on conditions explained below and assign it to two variable i.e. v_dte_meeting and v_status_meeting declared in my stored procedure,
Dte_Meeting| Ststus_Meeting
########################
15-Oct-14 | Due
30-Oct-14 | Due
15-Dec-14 | Init
30-Dec-14 | Init
30-Nov-15 | Approved
I want to assign value to these variables based on below conditions:
If a a single or multiple records present with Status_Meeting as 'Due' Then assign v_dte_meeting the greatest date with 'Due' status and assign v_status_meeting with value 'Due'
If above condition fails then, check If a single or multiple records present with Ststus_Meeting as 'Init' If it does, Then assign v_dte_meeting the greatest date with 'Init' status and assign v_status_meeting with value 'Init'
If both condition fails then assign both variables NULL value
Please help me to do it the best way in Oracle

Answer 1

Hope this helps. I am only showing the SELECT statement (I didn't create variables, so I am not selecting INTO, but that wasn't your difficulty, you know how to do that.) I use subquery factoring (the WITH clause), available only in versions >= 11 I believe, otherwise you can rewrite to put the subqueries where they belong.
Note the use of rank(); in Gordon's solution, he will pick up max(dte) over ALL rows, not just those with status = 'Due', so it can't be as simple as what he wrote. EDIT: I also don't see where he selects NULL, NULL if neither 'Due' nor 'Init' are present. (Sorry for the abuse, this should be a comment to his answer, I lack privileges.)
WITH t (Date_Meeting, Status_Meeting) AS
(
SELECT TO_DATE('15-OCT-14', 'DD-MON-YY'), 'Due' FROM dual UNION ALL
SELECT TO_DATE('30-OCT-14', 'DD-MON-YY'), 'Due' FROM dual UNION ALL
SELECT TO_DATE('15-DEC-14', 'DD-MON-YY'), 'Init' FROM dual UNION ALL
SELECT TO_DATE('30-DEC-14', 'DD-MON-YY'), 'Init' FROM dual UNION ALL
SELECT TO_DATE('15-NOV-15', 'DD-MON-YY'), 'Approved' FROM dual
),
s (Date_Meeting, Status_Meeting) AS
(
SELECT Date_Meeting, Status_Meeting FROM t
WHERE Status_Meeting = 'Due' OR Status_Meeting = 'Init'
UNION ALL SELECT NULL, NULL FROM dual -- To ensure you have the nulls if needed
),
r (Date_Meeting, Status_Meeting, rk) AS
(
SELECT Date_Meeting, Status_Meeting,
RANK() OVER (ORDER BY DECODE(Status_Meeting, 'Due', 0, 'Init', 1, 2),
Date_Meeting DESC) -- make sure you understand this
FROM s
)
SELECT Date_Meeting, Status_Meeting FROM r WHERE rk = 1
/
Result:
DATE_MEET STATUS_M
--------- --------
30-OCT-14 Due
1 row selected.

Answer 2

One method uses aggregation:
select (case when sum(case when status_meeting = 'Due' then 1 else 0 end) > 0
then max(case when status_meeting = 'Due' dte_meeting end)
when sum(case when status_meeting = 'Init' then 1 else 0 end) > 0
then max(case when status_meeting = 'Init' then dte_meeting end)
end),
(case when sum(case when status_meeting = 'Due' then 1 else 0 end) > 0
then'Due'
when sum(case when status_meeting = 'Init' then 1 else 0 end) > 0
then 'Init'
end)
into v_dte_meeting, v_status_meeting
from t;
However, I think a simpler version just uses order by:
select max(dte_meeting), max(status_meeting)
into v_dte_meeting, v_status_meeting
from (select t.*
from t
where status_meeting in ('Due', 'Init')
order by (case when status_meeting = 'Due' then 1
when status_meeting = 'Init' then 2
end)
) t
where rownum = 1;
The max() is just to ensure that exactly one row is returned.