Neat-o.
I think that's much better than the query I proposed with the
subselect. However, it doesn't give you price from the last sale of
the product, instead it gives you highest price the product was sold
for. Also, it can give you multiple rows for each product_code if
there are multiple sales at the same price.
Here is a small modification to Peter's query which will give you
exactly one row for each product code showing the price at the last
sale of that product. (Assuming you have a synthetic key, perhaps an
autoincrement field, called "id")
Also, an index on the product_code field will help the speed of this
query a lot. (I don't understand why the subselect query is still
faster - I don't think it should be.)
SQL is rather fun.
> SELECT t1.product_code,t1.date_sold,t1.price_sold
> FROM trans AS t1
> LEFT JOIN trans AS t2 ON t1.product_code = t2.product_code AND
> (t1.date_sold < t2.date_sold OR (t1.date_sold=t2.date_sold AND
> t1.id<t2.id)
> WHERE t2.product_code IS NULL
> ORDER BY t1.product_code;
Douglas Sims
Doug@stripped
On Sep 28, 2006, at 10:12 AM, Peter Brawley wrote:
> Mike,
>
>> What I need to do is find the last price_sold for each product_code.
>
> SELECT t1.product_code,t1.date_sold,t1.price_sold
> FROM trans AS t1
> LEFT JOIN trans AS t2 ON t1.product_code = t2.product_code AND
> t1.price_sold < t2.price_sold
> WHERE t2.product_code IS NULL
> ORDER BY t1.product_code;
>
> There's a bit of discussion at http://www.artfulsoftware.com/
> queries.php#7/
>
> PB
>
> -----
>
> mos wrote:
>> This should be easy but I can't find a way of doing it in 1 step.
>>
>> I have a Trans table like:
>>
>> Product_Code: X(10)
>> Date_Sold: Date
>> Price_Sold: Float
>>
>> Now there will be 1 row for each Product_Code, Date combination.
>> So over the past year a product_code could have over 300 rows, one
>> row for each day it was sold. There are thousands of products.
>>
>> What I need to do is find the last price_sold for each
>> product_code. Not all products are sold each day so a product
>> might not have been sold for weeks.
>>
>> The only solution I've found is to do:
>>
>> drop table if exists CurrentPrices;
>> create table CurrentPrices select Prod_Code, cast(max(Date_Sold)
>> as Date), -1.0 Price_Sold from Trans group by Prod_Code;
>> alter table CurrentPrices add index ix_ProdCode (Prod_Code);
>> update CurrentPrices CP, Trans T set CP.Price_Sold=T.Price_Sold
>> and T.Date_Sold=CP.Date_Sold;
>>
>> Is there a way to shorten this? It may take 2-3 minutes to
>> execute. I don't really need a new table as long as I get the
>> Prod_Code and the last Date_Sold.
>>
>> TIA
>> Mike
>>
>
>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.1.407 / Virus Database: 268.12.9/458 - Release Date:
> 9/27/2006
>
>
> --
> MySQL General Mailing List
> For list archives: http://lists.mysql.com/mysql
> To unsubscribe: http://lists.mysql.com/mysql?unsub=1
