Re: [Fwd: Re: no ORDER BY in subselects?]

At 11:50 21/09/00 -0400, Frank Bax wrote:
>At 11:29 AM 9/21/00 +1000, you wrote:
>>The main reason I use them is to find the 'next' or 'previous' record in a
>>list (eg. next date, next ID). eg.
>>
>>  select <whatever>, (select ID from table where id > this.id 
>>  order by id asc limit 1) as next_id ...
>
>Doesn't this give the same result (without order by):
>
>>  select <whatever>, (select min(ID) from table where id > this.id) as
>next_id

Yes, but I don't think PostgreSQL is smart enough to use indexes to
evaluate the Min() function. 

Also, min/max does not work quite so well with a slightly more complex
example:

 select <whatever>, (select ID from table where date_field > this.date_field      order by date_field asc limit 1) as
next_id...
 

(ie. if the date_field and id are not correlated, but you want the id
corresponding to the next date).



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