SQL sequence numbers and start/end date analysis - sql

Question

I am fairly new to SQL (SQL Management Studio 2016) and I only joined the site this morning...so my first post! I have been looking for a solution on the site regarding my issue. I have found a few links but none that (I think) will work having tried a few. I have a table that holds boiler service data. One address can have multiple dates/sequence numbers. I am looking to create a script that proves the latest sequential numbers start date is less than or equal to the latest sequential end date. So, in my example, I'd want to select the MAX seq_no for the start_date field and the 2nd MAX seq_no for the end_date field to make sure they haven't breached timescale.
My sample data has been added as an image (hopefully!)...just two addresses but there are 1000's in reality):
I have tried SLQ to get max seq_no's for just the end date initially but it just keeps bringing back all the entries:
select max (seq_no) as SEQNO, end_date, cmpnt_ref, prty_id
FROM hgmpcych
where prty_id in ('ABBEY10_TD12','ABBEY12_TD12') and cmpnt_ref='Boiler' and cycle_no='5'
group by end_date,prty_id,cmpnt_ref,seq_no
order by prty_id
This will probably be quite basic, but I am still pretty new to SQL. Any hints, advice or tips would be very much appreciated.

Answer 1

You could use ROW_NUMBER() to mark the rows in each group and only select the rows marked with 1 or 2 (The two "latest" rows)...
WITH
enumerated_hgmpcych AS
(
SELECT
seq_no, start_date, end_date, cmpnt_ref, prty_id,
ROW_NUMBER() OVER (PARTITION BY prty_id, cmpnt_ref
ORDER BY seq_no DESC
)
desc_seq_enumerator
FROM
hgmpcych
WHERE
prty_id in ('ABBEY10_TD12','ABBEY12_TD12')
AND cmpnt_ref='Boiler'
AND cycle_no='5'
)
SELECT
*
FROM
enumerated_hgmpcych
WHERE
desc_seq_enumerator <= 2
ORDER BY
prty_id,
cmpnt_ref,
seq_no
If you wanted to, you could collapse that to one row per group...
WITH
enumerated_hgmpcych AS
(
SELECT
seq_no, start_date, end_date, cmpnt_ref, prty_id,
ROW_NUMBER() OVER (PARTITION BY prty_id, cmpnt_ref
ORDER BY seq_no DESC
)
desc_seq_enumerator
FROM
hgmpcych
WHERE
prty_id in ('ABBEY10_TD12','ABBEY12_TD12')
AND cmpnt_ref='Boiler'
AND cycle_no='5'
)
SELECT
prty_id,
cmpnt_ref,
MAX(CASE WHEN desc_seq_enumerator = 1 THEN seq_no END) AS final_seq_no,
MAX(CASE WHEN desc_seq_enumerator = 1 THEN start_date END) AS final_start_date,
MAX(CASE WHEN desc_seq_enumerator = 1 THEN end_date END) AS final_end_date,
MAX(CASE WHEN desc_seq_enumerator = 2 THEN seq_no END) AS prev_seq_no,
MAX(CASE WHEN desc_seq_enumerator = 2 THEN start_date END) AS prev_start_date,
MAX(CASE WHEN desc_seq_enumerator = 2 THEN end_date END) AS prev_end_date
FROM
enumerated_hgmpcych
WHERE
desc_seq_enumerator <= 2
GROUP BY
prty_id,
cmpnt_ref
ORDER BY
prty_id,
cmpnt_ref

Answer 2

If you have max(seq_no), then you don't want it in the group by:
select max (seq_no) as SEQNO, end_date, cmpnt_ref, prty_id
from hgmpcych
where prty_id in ('ABBEY10_TD12', 'ABBEY12_TD12') and
cmpnt_ref = 'Boiler' and cycle_no = '5'
group by end_date, prty_id, cmpnt_ref
order by prty_id;