SQL select only highest date - sql

Question

For a project I want to generate a price list.
I want to get only the latest prices from each supplier for each article.
There are just those two tables.
Table articles
ARTNR | TXT | ACTIVE | SUPPLIER
------------------------------------------
10 | APPLE | Y | 10
20 | ORANGE | Y | 10
30 | KEYBOARD | N | 20
40 | ORANGE | Y | 20
50 | BANANA | Y | 10
60 | CHERRY | Y | 10
Table prices
ARTNR | PRCGRP | PRCDAT | PRICE
--------------------------------------
10 | 10 | 01-Aug-10 | 2.1
10 | 10 | 05-Aug-11 | 2.2
10 | 10 | 21-Aug-12 | 2.5
20 | 0 | 01-Aug-10 | 2.1
20 | 10 | 09-Aug-12 | 2.3
10 | 10 | 14-Aug-13 | 2.7
This is what I have so far:
SELECT
ARTICLES.[ARTNR], ARTICLES.[TXT], ARTICLES.[ACTIVE], ARTICLES.[SUPPLIER], PRICES.PRCGRP, PRICES.PRCDAT, PRICES.PRICE
FROM
ARTICLES INNER JOIN PRICES ON ARTICLES.ARTNR = PRICES.ARTNR
WHERE
(
(ARTICLES.[ACTIVE]="Y") AND
(ARTICLES.[SUPPLIER]=10) AND
(PRICES.PRCGRP=0) AND
(PRICES.PRCDAT=(SELECT MAX(PRCDAT) FROM PRICES as art WHERE art.ARTNR = PRICES.artnr) )
)
ORDER BY ARTICLES.ARTNR
;
It is okay to choose just one supplier each time, but I want the max price.
The problem is:
Lots of articles do not show up with the query above,
but I cannot figure out what is wrong.
I can see that they should be in the resultset when I leave out the subselect on max prcdat.
What is wrong?

Answer 1

Your subquery to get the latest price does not take the other conditions into account, that is when you're getting the latest price, you may get a price in another price group or that is not active. When you join that against the filtered list that has no inactive prices and only prices in a single price group, you get no hits that exist in both.
Either you need to duplicate or - better - move your conditions inside the subquery to get the best price under the conditions. I can't test against access, but something like this should be possible if the SQL is not too limited;
SELECT a.artnr, a.txt, a.active, a.supplier, p.prcgrp, p.prcdat, p.price
FROM articles a INNER JOIN prices p ON a.ARTNR = p.ARTNR
JOIN (
SELECT a.artnr, MAX(p.prcdat) prcdat
FROM articles a JOIN prices p ON a.artnr = p.artnr
WHERE a.active='Y' AND a.supplier=10 AND p.prcgrp=10
GROUP BY a.artnr) z
ON a.artnr = z.artnr AND p.prcdat = z.prcdat
ORDER BY a.ARTNR
If the SQL support in access won't allow a join with a subquery, you can just move the conditions inside your existing subquery, something like;
SELECT a.artnr, a.txt, a.active, a.supplier, p.prcgrp, p.prcdat, p.price
FROM articles a INNER JOIN prices p ON a.ARTNR = p.ARTNR
WHERE p.prcdat = (
SELECT MAX(p2.prcdat)
FROM articles a2 JOIN prices p2 ON a2.artnr = p2.artnr
WHERE a.artnr = a2.artnr AND a2.active='Y' AND a2.supplier=10 AND p2.prcgrp=10
)
ORDER BY a.ARTNR;
Note that due to limitations in identifying a unique price (no primary key in prices), the queries may give duplicates if several prices for the same article have the same prcdat. If that's a problem, you'll probably need to duplicate your conditions outside the subquery too.