使用“ in”緩慢的帶有聯接和子查詢的SQL嵌套集查詢

Question

我在慢速（〜4秒）的嵌套集結構上進行查詢時遇到了一些麻煩

select node.ID, node.Lft, node.Rgt, node.Level, count(ag.ArticleID) as count
from Webshop.Category node
left join Webshop.Category parent on parent.Lft between node.Lft and node.Rgt
left join Webshop.ArticleGroup ag on parent.GroupID = ag.GroupID
    and ag.ArticleID in (
        select a.ID
        from Webshop.Article a
        join Webshop.ArticleOwner ao on ao.ArticleID = a.ID and ao.OWNRID = 1
        join Webshop.ArticleAssortment aa on aa.ArticleID = a.ID and aa.AssortmentID = 6
    )
group by node.ID
having count > 0

說明返回以下內容：

id,select_type,table,type,possible_keys,key,key_len,ref,rows,Extra
1,PRIMARY,node,ALL,NULL,NULL,NULL,NULL,2538,"Using temporary; Using filesort"
1,PRIMARY,parent,ALL,Lft,NULL,NULL,NULL,2538,
1,PRIMARY,ag,ref,fk_ArticleGroup_Group1_idx,fk_ArticleGroup_Group1_idx,4,Webshop.parent.GroupID,9,"Using index"
2,"DEPENDENT SUBQUERY",a,eq_ref,PRIMARY,PRIMARY,4,func,1,"Using index"
2,"DEPENDENT     SUBQUERY",ao,eq_ref,"ArticleIDOWNRID,fk_ArticleOwner_Article1_idx,fk_ArticleOwner_OWNR1_idx",ArticleI    DOWNRID,8,"Webshop.a.ID,const",1,"Using index"
2,"DEPENDENT SUBQUERY",aa,eq_ref,"PRIMARY,fk_ArticleAssortment_Article1_idx",PRIMARY,8,"Webshop.a.ID,const",1,"Using index"

我認為使用in()的子查詢會使查詢變慢。 有一個更好的方法嗎？

謝謝。

編輯：

我忘記了從子查詢中的聯接中刪除left 。

Answer 1

您可以嘗試JOIN ：

select node.ID, node.Lft, node.Rgt, node.Level, count(ag.ArticleID) as count
from Webshop.Category node
left join Webshop.Category parent on parent.Lft between node.Lft and node.Rgt
left join Webshop.ArticleGroup ag on parent.GroupID = ag.GroupID
        join (
        select a.ID as `id`
        from Webshop.Article a
        left join Webshop.ArticleOwner ao on ao.ArticleID = a.ID and ao.OWNRID = 1
        left join Webshop.ArticleAssortment aa on aa.ArticleID = a.ID and aa.AssortmentID = 6
    ) in_ids on ag.ArticleID = in_ids.id
group by node.ID
having count > 0

Answer 2

首先，您在這里有大量的左聯接，並且左聯接很慢-我假設您正在使用它們，因為這里需要它們（即聯接的表可能不包含匹配項，並且您想返回Webshop的每一行。不論是否存在連接的行）。 如果不需要左聯接，我將轉換為內部聯接。 如果需要左連接，我會考慮更好的數據庫設計，以消除對這些左連接的需求。 這可能是不可避免的，但我會感到驚訝。

如果無法轉換為內部聯接，或者查詢仍然很慢，則可以嘗試先將子查詢作為插入語句運行，創建一個臨時表，然后使用該臨時表代替子查詢（可能是作為聯接而不是“ in”）。

如果仍然很慢，則可以嘗試在ID上索引該臨時表。

（在以上所有情況下，我都假定對表進行了合理索引？）

Answer 3

您的IN子查詢包含不影響結果的LEFT JOIN子句，因此首先您可以將其更改為：

select node.ID, node.Lft, node.Rgt, node.Level, count(ag.ArticleID) as count
from Webshop.Category node
left join Webshop.Category parent on parent.Lft between node.Lft and node.Rgt
left join Webshop.ArticleGroup ag on parent.GroupID = ag.GroupID
    and ag.ArticleID in (
        select a.ID
        from Webshop.Article a
    )
group by node.ID
having count > 0

現在，完成此操作后，我們可以看到您正在檢查AritcleID外鍵的一致性。 因此，有兩種選擇。 首先，有一個外鍵，您不必擔心，完全刪除IN ：

select node.ID, node.Lft, node.Rgt, node.Level, count(ag.ArticleID) as count
from Webshop.Category node
left join Webshop.Category parent on parent.Lft between node.Lft and node.Rgt
left join Webshop.ArticleGroup ag on parent.GroupID = ag.GroupID
group by node.ID
having count > 0

第二種選擇，您沒有外鍵。 創建一個不是一個壞主意。

更新：我剛剛注意到查詢的末尾有count > 0 ，這意味着您可以將所有left join子句替換為具有相同結果的inner join 。

在子查詢中用inner join left joins替換left joins ，唯一可能改變速度的是用EXISTS代替IN ：

select node.ID, node.Lft, node.Rgt, node.Level, count(ag.ArticleID) as count
from Webshop.Category node
inner join Webshop.Category parent on parent.Lft between node.Lft and node.Rgt
inner join Webshop.ArticleGroup ag on parent.GroupID = ag.GroupID
WHERE EXISTS (
    SELECT * FROM
        from Webshop.Article a
        join Webshop.ArticleOwner ao on ao.ArticleID = a.ID and ao.OWNRID = 1
        join Webshop.ArticleAssortment aa on aa.ArticleID = a.ID and aa.AssortmentID = 6 
    WHERE a.ID = ag.ArticleID
    )
group by node.ID
-- you don't need HAVING clause here