9

以下查询在 1.6 秒内执行

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)

添加AND shops.shop_id=86到最后的 WHERE 子句会导致查询在 292 秒内执行：

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)

我原以为限制商店表AND shops.shop_id=86会减少执行时间。相反，执行时间似乎取决于 products 表中 products.shop_id 等于指定的 shop.shop_id 的行数。products.shop_id=86 的 products 表中大约有 34K 行，执行时间为 292 秒。products.shop_id=50 大约有 28K 行，执行时间为 210 秒。products.shop_id=175，大约有2K行，执行时间为2.8秒。到底是怎么回事？

1.6 秒查询的 EXPLAIN EXTENDED 是：

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

此 EXPLAIN EXTENDED 的 SHOW WARNINGS 是

-----+
| 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 秒查询的 EXPLAIN EXTENDED 是：

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

此 EXPLAIN EXTENDED 的 SHOW WARNINGS 是

----+ 
| 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)) | 
+-----

我正在运行 MySQL 客户端版本：5.1.56。商店表在 shop_id 上有一个主索引：

Action  Keyname Type    Unique  Packed  Column  Cardinality Collation   Null    Comment
 Edit    Drop   PRIMARY BTREE   Yes No  shop_id 163 A

我已经分析了商店表，但这没有帮助。

我注意到，如果我删除LEFT JOIN执行时间的差异，则会下降到 0.12 秒而不是 0.28 秒。

Cez 的解决方案，即使用 1.6 秒版本的查询并通过添加rowed_results.shop_dummy=86到外部查询（如下所示）来删除不相关的结果，在 1.7 秒内执行。这规避了这个问题，但为什么 292 秒查询如此缓慢仍然是个谜。

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;
4

3 回答 3

1

您应该将 shop.shop_id=86 移动到商店的 JOIN 条件。没有理由把它放在 JOIN 之外，你冒着 MySQL JOINing 的风险，然后过滤。JOIN 可以完成与 WHERE 子句相同的工作，尤其是在您不引用其他表的情况下。

....
INNER JOIN shops ON shops.shop_id = p1.shop_id AND shops.shop_id=86
....

与性别加入相同的事情：

...
INNER JOIN shops ON shops.shop_id = p1.shop_id
AND sex.date >= SUBDATE(NOW(),INTERVAL 1 DAY)
...

派生表很棒，但它们没有索引。通常这无关紧要，因为它们通常在 RAM 中。但是在没有索引的过滤和排序之间，事情可以加起来。

请注意，在花费更长的第二个查询中，表处理顺序发生了变化。shop 表在慢查询中位于顶部，p1 表在快速查询中检索 11799 行而不是 1 行。它也不再使用主键。这很可能是你的问题所在。

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 p1  ref PRIMARY,shop_id,shop_id_2,product_id,shop_id_3  shop_id 4       11799   100.00
于 2012-11-16T02:55:27.493 回答
1

在聊天室之后，实际上创建了表/列来匹配查询，我想出了以下查询。

我已经开始我最内心的查询是关于性别、产品（对于 shop_id）和收藏夹表。由于您描述了 ShopA 的 ProductX = Product ID = 1 但 ShopB 的 ProductX = 产品 ID = 2（仅作为示例），因此每个商店的每个产品始终是唯一的，并且从不重复。也就是说，我可以在此查询中获取产品和 shop_id 以及收藏夹数量（如果有），但仅对 product_id 进行分组 .. 因为我使用 MAX() 的每个产品都不会更改 shop_id。由于您总是按“昨天”和性别（sex=0 女性）的日期查找，因此我会将 SEX 表编入索引（日期、性别、product_id）...我猜您不会每添加 1000 个项目天... 产品显然会在 product_id（主键）上有一个索引，而收藏夹应该在 product_id 上有一个索引。

然后，根据该结果（别名“sxFav”），我们可以通过该“Product_ID”直接连接到性别和产品表，以获取您可能想要的任何其他信息，例如商店名称、添加产品的日期、产品描述等. 然后，此结果按产品销售的 shop_id、日期和最后的产品 ID 排序（但您可以考虑在内部查询中获取描述列并将其用作排序依据）。这导致别名“PreQuery”。

由于商店的订单都是正确的，我们现在可以添加 @MySQLVariable 引用来为每个产品分配一个类似于您最初尝试的行号。但是，仅当商店 ID 更改时才重置回 1。

SELECT 
      PreQuery.*,
      @num := IF( @current_shop_id = PreQuery.shop_id, @num +1, 1 ) AS RowPerShop, 
      @current_shop_id := PreQuery.shop_id AS shop_dummy 
   from 
      ( SELECT 
              sxFav.product_id, 
              sxFav.shop_id, 
              sxFav.Favorites_Count
           from 
              ( SELECT 
                      sex.product_id,
                      MAX( p.shop_id ) shop_id,
                      SUM( CASE WHEN F.current = 1 AND F.closeted = 1 THEN 1 
                                WHEN F.current = 1 AND F.closeted = 0 THEN -1 
                                ELSE 0 END ) AS favorites_count 
                   from 
                      sex
                         JOIN products p
                            ON sex.Product_ID = p.Product_ID
                         LEFT JOIN Favorites F 
                            ON sex.product_id = F.product_ID 
                   where 
                          sex.date >= subdate( now(), interval 1 day) 
                      and sex.sex = 0 
                   group by 
                      sex.product_id ) sxFav 

              JOIN sex 
                 ON sxFav.Product_ID = sex.Product_ID

              JOIN products p
                 ON sxFav.Product_ID = p.Product_ID
      order by 
         sxFav.shop_id, 
         sex.date, 
         sxFav.product_id ) PreQuery,

     ( select @num :=0, 
              @current_shop_id := 0 ) as SQLVars

现在，如果您正在寻找特定的“分页”信息（例如每个商店 7 个条目），请将上面的 ENTIRE 查询包装成类似...

select * from ( entire query above ) where RowPerShop between 1 and 7

（或根据需要在 8 和 14、15 和 21 等之间）甚至

RowPerShop between RowsPerPage*PageYouAreShowing and RowsPerPage*(PageYouAreShowing +1)
于 2012-11-16T01:47:42.587 回答
1

从讨论来看，查询规划器在指定较低级别的商店时表现不佳。

添加rowed_results.shop_dummy=86到外部查询以获取您正在寻找的结果。

于 2012-11-16T00:53:45.023 回答