update pomocu subqueries u mysql-u

[ivanhoe]

imam 2 tabele koje se koriste za pravljenje statistike(jedna pamti svako pojedinacno glasanje, druga cuva izracunatu statistiku):

mysql> desc votes;
+---------+---------------------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------------+------+-----+-------------------+----------------+
| id | int(20) unsigned | NO | PRI | NULL | auto_increment |
| post_id | bigint(20) unsigned | NO | MUL | 0 | |
[... neka polja...]
| rank | tinyint(3) unsigned | NO | | 0 | |
+---------+---------------------+------+-----+-------------------+----------------+

mysql> desc post_details;
+----------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+---------------------+------+-----+---------+-------+
| post_id | bigint(20) unsigned | NO | PRI | 0 | |
[... neka polja...]
| rating | tinyint(3) unsigned | NO | MUL | 0 | |
| num_votes | int(10) | NO | | 0 | |
+----------------+---------------------+------+-----+---------+-------+


Posto je znatno porastao broj glasaca, dosadasnja praksa da se statistika updejtuje kod svakog glasanja vise nije dobra, nego mi je sad potrebno da pomocu cron taska updejtujem tu statistiku periodicno, tako sto cu izracunati:
SELECT AVG(rank), COUNT(*) FROM votes GROUP BY post_id;
i onda za svaki post upisati izracunate vrednosti u post_details.

Naravno ovo nije frka da se uradi programski u petlji, ali me zanima da li moze da se resi pomocu jednog upita( i koriscenjem subqueries pretpostavljam), posto cenim da moze, ali nisam uspeo da se snadjem kako...

ajd da vas cujem.. :D

EDIT: Uspeo sam u medjuvremenu da odradim ovo sa 2 upita:

UPDATE brush_details AS bd SET num_votes= (
SELECT count(*) FROM brush_votes AS bv WHERE bv.post_id=bd.post_id
);
UPDATE brush_details AS bd SET rating= (
SELECT avg(rank) FROM brush_votes AS bv WHERE bv.post_id=bd.post_id
);

Ali me i dalje zanima da li moze da se sve stavi u jedan?

[noviKorisnik]

Meni se čini da ne bi imao većih problema ako spojiš ova dva upita.
UPDATE brush_details AS bd
SET num_votes= (
SELECT count(*) FROM brush_votes AS bv WHERE bv.post_id=bd.post_id
), rating= (
SELECT avg(rank) FROM brush_votes AS br WHERE br.post_id=bd.post_id
);
Sad, ako ima gde da ovo testiraš ... javi. (Ok, ne vidim da se ovim postiže nešto ekstra u perfomansama, ali jedan je q)

[Dejan Topalovic]

Jesi probao ovako:
update post_details AS pd,
(SELECT AVG(rank) AS rting, COUNT(*) AS nm_votes FROM votes WHERE post_id = $post_id_var_u_phpu) AS v
SET rating = v.rting, num_votes = v.nm_votes
WHERE pd.post_id = $post_id_var_u_phpu;