minimum price on earliest date

Ok my first posted question :
(This is related to a travel website)

I have the following table layout :

CREATE TABLE "public"."package" (
"id" BIGINT NOT NULL,
"accom_code" VARCHAR(4) NOT NULL,
"start_date" DATE NOT NULL,
"end_date" DATE NOT NULL,
"pricing_type" VARCHAR(2),
"indic_price" NUMERIC(7,2),
"unit_price" NUMERIC(7,2),
"adult_age_max_cnt" INTEGER,
CONSTRAINT "package_pkey" PRIMARY KEY("id")
) WITH OIDS;

The package table contains a list (a very large one) for holiday accomodation packages.

What i'm trying to get is the following :

The MINIMUM price using the following for "price" :

CAST (CASE p.pricing_type
WHEN 'UN' THEN p.unit_price
WHEN 'PA' THEN p.indic_price*p.adult_age_max_cnt
ELSE p.unit_price
END AS NUMERIC(7,2))

AND

The minimum date (i.e. nearest start date) greater than today
WHERE the start_date equals the minimum start_date and the price equals the minimum price.

Any thoughts?

With any luck I will be able to give you an test data insert for this.

This should probably be posted in the POSTGRESQL section however I feel that it is a more general SQL question than anything else.What I have thus far :

SELECT p.accom_code
,MIN(CAST (CASE p.pricing_type
WHEN 'UN' THEN p.unit_price
WHEN 'PA' THEN p.indic_price*p.adult_age_max_cnt
ELSE p.indic_price
END AS NUMERIC(7,2))) as min_price
,MIN(p.start_date) as min_start
FROM package p
WHERE accom_code IN ('DDNA','ADE9','CGHH','ASEC','BDB9','HGMD','CMEF', 'BGDE','YRB5','BJAM')
AND p.duration = 7
AND start_date > current_date
AND start_date < current_date + interval '28 day'
GROUP BY p.accom_code

At the present time i'm getting 10 records (as expected). However I believe these records are WRONG as the minimum price doesn't necessarily match up with the minimum date for a particular (correct me i'm wrong here). How do I go about correcting this?|||Ooh think I nearly got it, can someone verify this :

SELECT p.accom_code
,x.min_start
,MIN(CAST (CASE p.pricing_type
WHEN 'UN' THEN p.unit_price
WHEN 'PA' THEN p.indic_price*p.adult_age_max_cnt
ELSE p.indic_price
END AS NUMERIC(7,2))) as min_price
FROM package p
JOIN (
SELECT p.accom_code,MIN(p.start_date) as min_start
FROM package p
WHERE accom_code IN ('DDNA','ADE9','CGHH','ASEC','BDB9','HGMD','CMEF', 'BGDE','YRB5','BJAM')
AND p.duration = 7
AND start_date > current_date
AND start_date < current_date + interval '28 day'
GROUP BY p.accom_code
) x
ON p.accom_code = x.accom_code AND x.min_start = p.start_date
WHERE p.accom_code IN ('DDNA','ADE9','CGHH','ASEC','BDB9','HGMD','CMEF', 'BGDE','YRB5','BJAM')
AND p.duration = 7
AND start_date > current_date
AND start_date < current_date + interval '28 day'
GROUP BY p.accom_code,x.min_start

In theory it should give the cheapest price on the earliest start date for each of the 10 accomodation types.

Edit : Just to finish it off I needed the start_date out of it as well ;) (added x.min_start to select and group clause)|||looks okay to me

i would not use the same alias "p" in more than one place in the query

and i would probably remove one of the following:AND p.duration = 7
AND p.duration = 7;)|||LOL oh yeah. I've cleaned it up in the above post now.
However I do have one question to finish it off (and this annoys me about of lot of SQL i've done in the past) :
Is there any way to remove the duplicate WHERE clauses in a query like this, and somehow apply it only once but for both sections? I hope that question makes sense.|||Is there any way to remove the duplicate WHERE clauses in a query like thisdefine a view|||Btw, your queries won't work at all in SQL because you used delimited schema/table/column names in the CREATE TABLE statement (i.e. double-quotes) but not in your query.|||That DDL was written in PMS for Postgres so it's a pure copy. I did mention that I was using Postgresql in my first post.

What I DID want to be standard was the SQL query I was doing. :D|||Well, then you have to use delimited schema/table/column names in your query - as I said.|||I have come across a problem with the query above. If two records calculate the same minimum price for one accom_code I can get two results when joined to itself.
i.e. min price and min date is £189 and 25/05/07
when self-joined total price = £567 / 3 adults = £189
and total price = £378 / 2 adults = £189

They both match the minimum price and date and thus both records are output. DOH!

As a quick hack (and I don't like this method) I did a distinct and ordered by total price minimum first.|||Is there any way to remove the duplicate WHERE clauses in a query like this, and somehow apply it only once but for both sections?
For this purpose, SQL99 defines "common table expressions", i.e., a "WITH" subclause of a select statement. Not yet available in the current version of PostgreSQL but coming soon (8.4 probably) ;)
(DB2, Oracle and SQLServer already have them in place.)
Your query, with CTEs, would become:WITH p AS
( SELECT accom_code, start_date,
MIN(CAST (CASE pricing_type
WHEN 'UN' THEN unit_price
WHEN 'PA' THEN indic_price*adult_age_max_cnt
ELSE indic_price
END AS NUMERIC(7,2))) as min_price
FROM package
WHERE accom_code IN ('DDNA','ADE9','CGHH','ASEC',
'BDB9','HGMD','CMEF','BGDE','YRB5','BJAM')
AND duration = 7
AND start_date > current_date
AND start_date < current_date + interval '28 day'
),
x AS
( SELECT p.accom_code,MIN(p.start_date) as min_start
FROM p
GROUP BY p.accom_code
)
SELECT p.accom_code,x.min_start,p.min_price
FROM p INNER JOIN x
ON p.accom_code = x.accom_code AND x.min_start = p.start_date
GROUP BY p.accom_code,x.min_start
These are effectively "local view definitions", cf suggestion by r937.
(Note that in the above query, the SELECT .. p.min_price is not compatible with the GROUP BY -- maybe add p.min_price to the GROUP BY? Or replace it by "MIN(p.min_price)"?)sql