Baron Schwartz wrote:
> Hi,
>
> Afan Pasalic wrote:
>>
>> Baron Schwartz wrote:
>>> Hi Afan,
>>>
>>> Afan Pasalic wrote:
>>>> hi,
>>>> if I have column order_id(int(4)) null do I have to index it too.
>>>> I'm going to use it ONLY for sorting records.
>>>
>>> It depends a lot on how much data is in the table, etc etc. An
>>> index will make sorting more efficient in the general case when you
>>> have a decent amount of data. But it's hard to be specific with so
>>> little information.
>>>
>>> Baron
>>>
>> I have table products (product_id is PK). I have table categories
>> (cat_id is PK). since the product can be in more than one category, I
>> have prod_cat table:
>> create prod_cat(
>> cat_id int(8) unsigned not null,
>> prod_id int(8) unsigned not null,
>> order_id int(4) unsigned null,
>> PRIMARY KEY (cat_id, prod_id)
>> ) engine=Innodb;
>>
>
> Okay, so your order_id is really sort order, not "id of the customer's
> request to buy something." (As an aside, perhaps "sort_order" would
> confuse you less in the future when you don't remember the column's
> purpose anymore).
>
> It probably makes sense to index the column if you want to use it for
> sorting. You could also just order by the primary key. But I
> understand there are times when you want to have a different ordering.
>
> Baron
yes, you're right. sort_order does make more sense :)
order by PK, in my case is, let's say impossible because I'm sorting
products in ONE category. e.g.:
cat_id | prod_id | order_id
1 | 23 | 1
1 | 25 | 2
1 | 36 | 3
1 | 13 | 4
2 | 13 | 1
2 | 45 | 2
2 | 47 | 3
2 | 51 | 4
3 | 32 | 1
3 | 33 | 2
3 | 34 | 3
3 | 35 | 4
-afan
