la seguente query viene eseguita in 1,6 secondiPerché questa clausola WHERE rende la mia query 180 volte più lenta?
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
#this query limits the results of the query within it by row number (so that only 250 products get displayed per store)
SELECT * FROM (
#this query adds row numbers to the query within it
SELECT *, @num := IF(@current_shop_id = shop_id, IF(@current_product_id=product_id,@num,@num+1), 0) AS row_number, @current_shop_id := shop_id AS shop_dummy, @current_product_id := product_id AS product_dummy FROM (
SELECT shop, shops.shop_id AS
shop_id, p1.product_id AS
product_id
FROM products p1 LEFT JOIN #this LEFT JOIN gets the favorites count for each product
(
SELECT fav3.product_id AS product_id, SUM(CASE
WHEN fav3.current = 1 AND fav3.closeted = 1 THEN 1
WHEN fav3.current = 1 AND fav3.closeted = 0 THEN -1
ELSE 0
END) AS favorites_count
FROM favorites fav3
GROUP BY fav3.product_id
) AS fav4 ON p1.product_id=fav4.product_id
INNER JOIN sex ON sex.product_id=p1.product_id AND
sex.sex=0 AND
sex.date >= SUBDATE(NOW(),INTERVAL 1 DAY)
INNER JOIN shops ON shops.shop_id = p1.shop_id
ORDER BY shop, sex.DATE, product_id
) AS testtable
) AS rowed_results WHERE
rowed_results.row_number>=0 AND
rowed_results.row_number<(7)
aggiungendo AND shops.shop_id=86
alla finale clausola WHERE fa sì che la query da eseguire in 292 secondi:
SET @num :=0, @current_shop_id := NULL, @current_product_id := NULL;
#this query limits the results of the query within it by row number (so that only 250 products get displayed per store)
SELECT * FROM (
#this query adds row numbers to the query within it
SELECT *, @num := IF(@current_shop_id = shop_id, IF(@current_product_id=product_id,@num,@num+1), 0) AS row_number, @current_shop_id := shop_id AS shop_dummy, @current_product_id := product_id AS product_dummy FROM (
SELECT shop, shops.shop_id AS
shop_id, p1.product_id AS
product_id
FROM products p1 LEFT JOIN #this LEFT JOIN gets the favorites count for each product
(
SELECT fav3.product_id AS product_id, SUM(CASE
WHEN fav3.current = 1 AND fav3.closeted = 1 THEN 1
WHEN fav3.current = 1 AND fav3.closeted = 0 THEN -1
ELSE 0
END) AS favorites_count
FROM favorites fav3
GROUP BY fav3.product_id
) AS fav4 ON p1.product_id=fav4.product_id
INNER JOIN sex ON sex.product_id=p1.product_id AND
sex.sex=0 AND
sex.date >= SUBDATE(NOW(),INTERVAL 1 DAY)
INNER JOIN shops ON shops.shop_id = p1.shop_id AND
shops.shop_id=86
ORDER BY shop, sex.DATE, product_id
) AS testtable
) AS rowed_results WHERE
rowed_results.row_number>=0 AND
rowed_results.row_number<(7)
avrei pensato che limita la tavola negozi con AND shops.shop_id=86
sarebbe ridurre i tempi di esecuzione. Invece, il tempo di esecuzione sembra dipendere dal numero di righe nella tabella prodotti con products.shop_id uguale al negozi.shop_id specificato. Nella tabella prodotti sono presenti circa 34.000 righe con products.shop_id = 86 e il tempo di esecuzione è 292 secondi. Per products.shop_id = 50, ci sono circa 28K righe e il tempo di esecuzione è 210 secondi. Per products.shop_id = 175, ci sono circa 2K righe e il tempo di esecuzione è di 2,8 secondi. Cosa sta succedendo?
spiegare meteo per la seconda query 1.6 sono:
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 1203 100.00 Using where
2 DERIVED <derived3> ALL NULL NULL NULL NULL 1203 100.00
3 DERIVED sex ALL product_id_2,product_id NULL NULL NULL 526846 75.00 Using where; Using temporary; Using filesort
3 DERIVED p1 eq_ref PRIMARY,shop_id,shop_id_2,product_id,shop_id_3 PRIMARY 4 mydatabase.sex.product_id 1 100.00
3 DERIVED <derived4> ALL NULL NULL NULL NULL 14752 100.00
3 DERIVED shops eq_ref PRIMARY PRIMARY 4 mydatabase.p1.shop_id 1 100.00
4 DERIVED fav3 ALL NULL NULL NULL NULL 15356 100.00 Using temporary; Using filesort
Mostra avvisi per Questo spiega estesa è
-----+
| Note | 1003 | select `rowed_results`.`shop` AS `shop`,`rowed_results`.`shop_id` AS `shop_id`,`rowed_results`.`product_id` AS `product_id`,`rowed_results`.`row_number` AS `row_number`,`rowed_results`.`shop_dummy` AS `shop_dummy`,`rowed_results`.`product_dummy` AS `product_dummy` from (select `testtable`.`shop` AS `shop`,`testtable`.`shop_id` AS `shop_id`,`testtable`.`product_id` AS `product_id`,(@num:=if(((@current_shop_id) = `testtable`.`shop_id`),if(((@current_product_id) = `testtable`.`product_id`),(@num),((@num) + 1)),0)) AS `row_number`,(@current_shop_id:=`testtable`.`shop_id`) AS `shop_dummy`,(@current_product_id:=`testtable`.`product_id`) AS `product_dummy` from (select `mydatabase`.`shops`.`shop` AS `shop`,`mydatabase`.`shops`.`shop_id` AS `shop_id`,`mydatabase`.`p1`.`product_id` AS `product_id` from `mydatabase`.`products` `p1` left join (select `mydatabase`.`fav3`.`product_id` AS `product_id`,sum((case when ((`mydatabase`.`fav3`.`current` = 1) and (`mydatabase`.`fav3`.`closeted` = 1)) then 1 when ((`mydatabase`.`fav3`.`current` = 1) and (`mydatabase`.`fav3`.`closeted` = 0)) then -(1) else 0 end)) AS `favorites_count` from `mydatabase`.`favorites` `fav3` group by `mydatabase`.`fav3`.`product_id`) `fav4` on(((`mydatabase`.`p1`.`product_id` = `mydatabase`.`sex`.`product_id`) and (`fav4`.`product_id` = `mydatabase`.`sex`.`product_id`))) join `mydatabase`.`sex` join `mydatabase`.`shops` where ((`mydatabase`.`sex`.`sex` = 0) and (`mydatabase`.`p1`.`product_id` = `mydatabase`.`sex`.`product_id`) and (`mydatabase`.`shops`.`shop_id` = `mydatabase`.`p1`.`shop_id`) and (`mydatabase`.`sex`.`date` >= (now() - interval 1 day))) order by `mydatabase`.`shops`.`shop`,`mydatabase`.`sex`.`date`,`mydatabase`.`p1`.`product_id`) `testtable`) `rowed_results` where ((`rowed_results`.`row_number` >= 0) and (`rowed_results`.`row_number` < 7)) |
+------
spiegare meteo per la seconda query 292 è:
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 36 100.00 Using where
2 DERIVED <derived3> ALL NULL NULL NULL NULL 36 100.00
3 DERIVED shops const PRIMARY PRIMARY 4 1 100.00 Using temporary; Using filesort
3 DERIVED p1 ref PRIMARY,shop_id,shop_id_2,product_id,shop_id_3 shop_id 4 11799 100.00
3 DERIVED <derived4> ALL NULL NULL NULL NULL 14752 100.00
3 DERIVED sex eq_ref product_id_2,product_id product_id_2 5 mydatabase.p1.product_id 1 100.00 Using where
4 DERIVED fav3 ALL NULL NULL NULL NULL 15356 100.00 Using temporary; Using filesort
SHOW WARNINGS per questo EXPLAIN EXTENDED è
----+
| Note | 1003 | select `rowed_results`.`shop` AS `shop`,`rowed_results`.`shop_id` AS `shop_id`,`rowed_results`.`product_id` AS `product_id`,`rowed_results`.`row_number` AS `row_number`,`rowed_results`.`shop_dummy` AS `shop_dummy`,`rowed_results`.`product_dummy` AS `product_dummy` from (select `testtable`.`shop` AS `shop`,`testtable`.`shop_id` AS `shop_id`,`testtable`.`product_id` AS `product_id`,(@num:=if(((@current_shop_id) = `testtable`.`shop_id`),if(((@current_product_id) = `testtable`.`product_id`),(@num),((@num) + 1)),0)) AS `row_number`,(@current_shop_id:=`testtable`.`shop_id`) AS `shop_dummy`,(@current_product_id:=`testtable`.`product_id`) AS `product_dummy` from (select 'shop.nordstrom.com' AS `shop`,'86' AS `shop_id`,`mydatabase`.`p1`.`product_id` AS `product_id` from `mydatabase`.`products` `p1` left join (select `mydatabase`.`fav3`.`product_id` AS `product_id`,sum((case when ((`mydatabase`.`fav3`.`current` = 1) and (`mydatabase`.`fav3`.`closeted` = 1)) then 1 when ((`mydatabase`.`fav3`.`current` = 1) and (`mydatabase`.`fav3`.`closeted` = 0)) then -(1) else 0 end)) AS `favorites_count` from `mydatabase`.`favorites` `fav3` group by `mydatabase`.`fav3`.`product_id`) `fav4` on(((`fav4`.`product_id` = `mydatabase`.`p1`.`product_id`) and (`mydatabase`.`sex`.`product_id` = `mydatabase`.`p1`.`product_id`))) join `mydatabase`.`sex` join `mydatabase`.`shops` where ((`mydatabase`.`sex`.`sex` = 0) and (`mydatabase`.`sex`.`product_id` = `mydatabase`.`p1`.`product_id`) and (`mydatabase`.`p1`.`shop_id` = 86) and (`mydatabase`.`sex`.`date` >= (now() - interval 1 day))) order by 'shop.nordstrom.com',`mydatabase`.`sex`.`date`,`mydatabase`.`p1`.`product_id`) `testtable`) `rowed_results` where ((`rowed_results`.`row_number` >= 0) and (`rowed_results`.`row_number` < 7)) |
+-----
Sto eseguendo la versione client MySQL: 5.1.56. La tabella di negozi ha un indice primario su shop_id:
Action Keyname Type Unique Packed Column Cardinality Collation Null Comment
Edit Drop PRIMARY BTREE Yes No shop_id 163 A
ho analizzato la tabella negozio, ma questo non ha aiutato.
Ho notato che se rimuovo lo LEFT JOIN
la differenza nei tempi di esecuzione scende a 0,12 secondi rispetto a 0,28 secondi.
La soluzione di Cez, ovvero utilizzare la versione 1.6 secondi della query e rimuovere risultati irrilevanti aggiungendo rowed_results.shop_dummy=86
alla query esterna (come di seguito), viene eseguita in 1,7 secondi. Ciò aggira il problema, ma il mistero rimane il motivo per cui una query di 292 secondi è così lenta.
Qual è l'uscita di "spiegano EXTENDED .." seguito da "MOSTRA AVVERTENZE"? –
Cez
... per entrambe le versioni della dichiarazione? Confronta le uscite di 'EXPLAIN' per vedere qual è la differenza. Inoltre tutte le colonne in una singola clausola 'WHERE' dovrebbero entrare in una chiave. – feeela
@Cez @feela grazie per il promemoria, ho aggiunto le query "EXPLAIN EXTENDED' alla domanda. 'SHOW WARNINGS' non ha prodotto risultati. – jela