Get only best ranked rows from a subquery - sql

Question

I want to get the price of an article for a specific customer.
There are several levels of prices which i ranked in my query.
So Article A has a price on rank 1, 4, 6. The result should always be the lowest ranked price.
Article B rank 3 ,5
So article A price is ranked 1 and Article b is price ranked 3.
My query is below .
SELECT p2.* FROM(
SElect ART_ID, MIN(RANG) RANG FROM (
Select p.ART_ID, p.betrag ,
CASE p.PREIS_EBENE WHEN 'KA' THEN 1 WHEN 'KW' THEN 2 WHEN 'W' THEN 7 WHEN 'A' THEN 6 ELSE 99 END RANG
FROM MDART a
INNER JOIN MDPRSVK p ON (a.KLIENT_ID = p.KLIENT_ID AND a.ART_ID = p.ART_ID)
WHERE ICP_KZ.IS_SET(KENNUNG_USER, 'P') = 1
ORDER BY RANG)
GROUP BY ART_ID) T
INNER JOIN MDPRSVK p2 ON (p2.ART_ID = T.ART_ID AND p2.PREIS_EBENE = p.PREIS_EBENE)
i want to have every article appearing only once in the result

Answer 1

You have tagged your request PL/SQL, so I guess your DBMS may be Oracle.
If I understand correctly, the table MDPRSVK contains several prices per ART_ID. And you want to select each ART_ID's best price (best to worst: 'KA' -> 'KW' -> 'A' -> 'W' -> any other PREIS_EBENE).
You can use a window function (ROW_NUMBER, RANK or DENSE_RANK) for this:
select *
from mdprsvk
order by row_number()
over (partition by art_id
order by decode(preis_ebene, 'KA', 1, 'KW', 2, 'A', 3, 'W', 4, 5))
fetch first row with ties;
This is standard SQL. In Oracle, FETCH FIRST is available as of version 12c. In earlier versions you'd use a subquery instead:
select *
from
(
select
mdprsvk.*,
row_number() over (partition by art_id
order by decode(preis_ebene, 'KA', 1, 'KW', 2, 'A', 3, 'W', 4, 5))
as rn
from mdprsvk
)
where rn = 1;
Or use OraclesKEEP FIRST`:
select art_id, max(betrag)
keep (dense_rank first
order by decode(preis_ebene, 'KA', 1, 'KW', 2, 'A', 3, 'W', 4, 5))
from mdprsvk
group by art_id;
It is not clear, how MDART comes into play. It looks like you want to restrict your results to articles for certain clients and KENNUNG_USER is the column in MDART to check. If so, add a WHERE clause:
where exists
(
select *
from mdart
where mdart.klient_id = mdprsvk.klient_id
and mdart.art_id = mdprsvk.art_id
and icp_kz.is_set(mdart.kennung_user, 'p') = 1
)
Or with IN instead of EXISTS:
where (klient_id, art_id) in
(
select klient_id, art_id
from mdart
where icp_kz.is_set(kennung_user, 'p') = 1
)