次のクエリは1.6秒で実行されます
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)
最後のWHERE句に追加AND shops.shop_id=86すると、クエリは292秒で実行されます。
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)
AND shops.shop_id=86ショップテーブルを制限すると、実行時間が短縮されると思いました。代わりに、実行時間は、products.shop_idが指定されたshops.shop_idと等しいproductsテーブルの行数に依存しているように見えます。products.shop_id = 86のproductsテーブルには約34Kの行があり、実行時間は292秒です。products.shop_id = 50の場合、約28K行あり、実行時間は210秒です。products.shop_id = 175の場合、約2K行あり、実行時間は2.8秒です。何が起こっている？
1.6秒のクエリに対して拡張されたEXPLAINは次のとおりです。
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
このEXPLAINEXTENDEDの警告を表示する
-----+
| 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)) |
+------
292秒のクエリに対して拡張されたEXPLAINは次のとおりです。
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
このEXPLAINEXTENDEDの警告を表示する
----+
| 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)) |
+-----
MySQLクライアントバージョン5.1.56を実行しています。ショップテーブルには、shop_idにプライマリインデックスがあります。
Action Keyname Type Unique Packed Column Cardinality Collation Null Comment
Edit Drop PRIMARY BTREE Yes No shop_id 163 A
ショップテーブルを分析しましたが、役に立ちませんでした。
LEFT JOIN実行時間の差を取り除くと、0.28秒に対して0.12秒に低下することに気付きました。
Cezのソリューション、つまり、クエリの1.6秒バージョンを使用rowed_results.shop_dummy=86し、外部クエリに追加して無関係な結果を削除する（以下のように）、1.7秒で実行されます。これは問題を回避しますが、なぜ292秒のクエリが非常に遅いのかという謎が残っています。
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
INNER JOIN shops ON shops.shop_id = p1.shop_id
WHERE sex.date >= SUBDATE(NOW(),INTERVAL 1 DAY)
ORDER BY shop, sex.DATE, product_id
) AS testtable
) AS rowed_results WHERE
rowed_results.row_number>=0 AND
rowed_results.row_number<(7) AND
rowed_results.shop_dummy=86;