Thank you very much for your reply. I'll try to modify it.
Josh Berkus wrote:
> Hannes,
>
>
>>The query and the corresponding EXPLAIN is at
>>
>>http://hannes.imos.net/query.txt
>
>
> The problem is that you're using a complex corellated sub-select in the SELECT
> clause:
>
> SELECT
> d.delivery_id,
> da.article_no,
> da.amount,
> (
> SELECT
> COUNT(*)
> FROM
> serials s
> INNER JOIN rma_ticket_serials rts ON (
> s.serial_id = rts.serial_id
> )
> WHERE
> s.article_no = da.article_no AND
> s.delivery_id = d.delivery_id AND
> rts.replace = FALSE
> ) AS replaced_serials
>
> This means that the planner pretty much has to iterate over the subquery,
> running it once for each row in the result set. If you want the optimizer
> to use a JOIN structure instead, put the subselect in the FROM clause.
>
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