Re: aggregate / group by question - Mailing list pgsql-sql

T E Schmitz wrote:

> Hello,
> I must apologize for not coming up with a more descriptive subject line.
>
> I am struggling with the following query and I am not even sure 
> whether what I want to achieve is possible at all:
>
> The problem in real-world terms: The DB stores TRANSAKTIONS - which 
> are either sales or refunds: each TRANSAKTION has n ITEMS related to 
> it, which contain their RETAIL_PRICE and DISCOUNT. At the end of day, 
> a total is run up, which should show the sum of refunds, sales and 
> discounts.
>
> Tables:
>
> TRANSAKTION
> -----------
> KIND ('R' or 'S' for refund or sale)
> TRANSAKTION_PK
> PAYMENT_METHOD (cheque, cash, CC)
>
> ITEM
> ----
> TRANSAKTION_FK
> ITEM_PK
> RETAIL_PRICE
> DISCOUNT
>
> Desired result set:
>
> PAYMENT_METHOD | category | SUBTOTAL
> ------------------------------------
> Cash           | sales    | 103,55
> Cash           | discounts|  -0,53
> Cash           | refunds  | -20,99
> CC             | sales    | 203,55
> CC             | discounts|  -5,53
> CC             | refunds  | -25,99
>
> where
> sales amount is the sum of RETAIL_PRICE
> discount amount is the sum of DISCOUNT
> refunds is the sum of (RETAIL_PRICE-DISCOUNT)
>
>
> I've had a stab at it but my sales amount is short of the 
> RETAIL_PRICEs of all discounted ITEMs:
>
>
> select PAYMENT_METHOD,
> case
> when KIND='R' then 'R'
> when KIND='S' and DISCOUNT is not null then 'D'
> when KIND='S' and DISCOUNT is  null then 'S'
> end as CATEGORY,
>
> sum(case
> when KIND=2 then -(RETAIL_PRICE-coalesce(DISCOUNT,0))
> when KIND=1 and DISCOUNT is not null then -DISCOUNT
> when KIND=1 and DISCOUNT is null then RETAIL_PRICE
> end) as SUBTOTAL,
>
> from ITEM
> inner join TRANSAKTION on TRANSAKTION_PK =TRANSAKTION_FK
>
> where ...
>
> group by PAYMENT_METHOD,CATEGORY
> order by PAYMENT_METHOD,CATEGORY
>
Your comment implies that the amount of retail sales is the sum of all 
amounts regardless of whether or not discount IS NULL.  So perhaps 
losing the 'IS NULL' from you retail_price case may fix your statement.  
If not...

This may be a bit heavy handed AND I am still a novice AND I am not on 
my system so I can't test it but how about

SELECT merged_data.payment_method,      merged_data.category,      merged_data.subtotal FROM (
--       Get the refunds.  (kind = 'R')        SELECT transaktion.payment_method,               'refunds' AS category,
            -1 * sum( item.retail_price - COALESCE(item.discount) ) 
 
AS subtotal          FROM transaktion          LEFT OUTER JOIN item            ON ( transaktion.transaktion_pk =
item.transaktion_fk)         WHERE transaktion.kind = 'R'         GROUP BY transaktion.payment_method        UNION ALL
 
--       Get the sales.  (kind = 'S')        SELECT transaktion.payment_method,               'sales' AS category,
        sum( item.retail_price - COALESCE(item.discount, 0) ) AS 
 
subtotal          FROM transaktion          LEFT OUTER JOIN item            ON ( transaktion.transaktion_pk =
item.transaktion_fk)         WHERE transaktion.kind = 'S'         GROUP BY transaktion.payment_method        UNION ALL
 
--         Get the discounts.  (kind = 'S' AND discount IS NOT NULL)        SELECT transaktion.payment_method,
    'discounts' AS category,               -1 * sum( COALESCE(item.discount, 0) ) AS subtotal          FROM transaktion
        LEFT OUTER JOIN item            ON ( transaktion.transaktion_pk = item.transaktion_fk )         WHERE
transaktion.kind= 'S'           AND transaktion.discount IS NOT NULL         GROUP BY transaktion.payment_method      )
ASmerged_dataORDER BY merged_data.payment_method,         merged_data.category;
 

--
HTH

Kind Regards,
Keith