In article <4CE2688B.2050000@xxxxxxxxxxxx>,
Arjen van der Meijden <acmmailing@xxxxxxxxxxxx> writes:
> On 16-11-2010 11:50, Louis-David Mitterrand wrote:
>> I have to collect lots of prices from web sites and keep track of their
>> changes. What is the best option?
>>
>> 1) one 'price' row per price change:
>>
>> create table price (
>> id_price primary key,
>> id_product integer references product,
>> price integer
>> );
>>
>> 2) a single 'price' row containing all the changes:
>>
>> create table price (
>> id_price primary key,
>> id_product integer references product,
>> price integer[] -- prices are 'pushed' on this array as they change
>> );
>>
>> Which is bound to give the best performance, knowing I will often need
>> to access the latest and next-to-latest prices?
> If you mostly need the last few prices, I'd definitaly go with the
> first aproach, its much cleaner. Besides, you can store a date/time
> per price, so you know when it changed. With the array-approach that's
> a bit harder to do.
I'd probably use a variant of this:
CREATE TABLE prices (
pid int NOT NULL REFERENCES products,
validTil timestamp(0) NULL,
price int NOT NULL,
UNIQUE (pid, validTil)
);
The current price of a product is always the row with validTil IS NULL.
The lookup should be pretty fast because it can use the index of the
UNIQUE constraint.
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