我在查询

Question

几个月前我写了这个查询。它运行良好。但是，这种查询日复一日地执行得越来越慢。

除了相同的表执行之外，此查询还检查多个表中的帐单历史记录。

这是查询 -

SELECT * FROM (
            SELECT *,                
            (SELECT username FROM users WHERE id = u_bills.UserId) AS username,
            (SELECT first_name FROM users WHERE id = u_bills.UserId) AS first_name,
            (SELECT last_name FROM users WHERE id = u_bills.UserId) AS last_name,
            (SELECT phone FROM users WHERE id = u_bills.UserId) AS phone,
            (SELECT email FROM users WHERE id = u_bills.UserId) AS email,
            (SELECT CPRate FROM cpt WHERE UserId = u_bills.UserId ORDER BY AddedDate DESC LIMIT 0,1) AS cprate,
            (SELECT (SELECT PopName FROM pops WHERE PopId = p.PopName) AS PopFullName FROM u_setupinfos AS p 
            WHERE UserId = u_bills.UserId) AS popname,
            (SELECT active FROM users WHERE id = u_bills.UserId) AS active,                
            (SELECT SUM(PaidAmount) AS PaidAmount FROM u_billhistory 
            WHERE UserId = u_bills.UserId AND MONTH(AddedDate) = MONTH(PaidDate)) AS PaidAmount,
            (SELECT PaidDate FROM u_billhistory 
             WHERE UserId = u_bills.UserId AND MONTH(AddedDate) = MONTH(PaidDate) 
             GROUP BY MONTH(PaidDate)) AS PaidDate,
            (SELECT PaymentMedia FROM u_billhistory 
            WHERE UserId = u_bills.UserId AND MONTH(AddedDate) = MONTH(PaidDate) 
            GROUP BY MONTH(PaidDate)) AS PaymentMedia,   
    (SELECT TransactionId FROM u_billhistory 
            WHERE UserId = u_bills.UserId AND MONTH(AddedDate) = MONTH(PaidDate) GROUP BY MONTH(PaidDate)) AS TransactionId,
            (SELECT GROUP_CONCAT(CONCAT(`BillHisId`,';',`PaidAmount`,';',`PaidDate`) separator '|') AS vals 
FROM u_billhistory 
WHERE UserId = u_bills.UserId 
AND YEAR(PaidDate) = YEAR(CURDATE())) AS TotalPaids
            FROM u_bills) AS m
        WHERE m.username = 'abc'

请查看图片上的EXPLAIN报告 -

我想组织这个查询。我需要建议使这个查询更快，如3到5秒，而不是1分半钟或更长。我在这个问题上犯了什么错误？

重要提示 -

我在查询

上使用了几乎每个列的索引

Answer 1

这很慢，因为你让它为结果中每条记录的每个字段单独查找一个附加表...有时不止一个。您应该使用JOIN而不是嵌套的SELECT。对于某些分组结果，您可以加入SELECT语句，该语句执行自己的GROUP BY。

此外，各列上的单独索引请勿帮助!!

将索引想象成电话簿。一个简单的电话簿在姓氏和名字上使用聚集索引。然后它还列出了每个项目的地址和电话号码。这就是聚集索引：只是数据的存储顺序。

其他索引就像补充一样。 “电话号码”上的非聚集索引就像本书末尾的补充，按顺序列出电话号码，然后显示姓氏和名字（但不是地址）。 “地址”的索引也会这样做：一个单独的补充，按顺序列出地址，然后给你起名字。

使用这些索引补充，如果您有一个电话号码并想知道地址，您必须首先查找补充中的电话号码以查找名称，然后在主书中查找名称以获取地址。在此示例中，电话补充确实有帮助，因为它比电话簿的完整扫描更好。

但是，重要的是要注意地址补充_does 不帮助此搜索，即使地址是您想要找到的确切字段。可能对其他搜索有用，但在这种情况下无效。此外，请记住，对您图书的每次更新都要求您不仅要更新图书，还要更新所有补充内容。它不仅仅是存储空间，还包括更新每个索引所花费的时间。你需要考虑它是否值得。如果你有一堆未使用的索引，没有它们你会更好。

回到你的具体问题，关于唯一真正对你有帮助的索引是u_bills.username，user.UserId（希望它的表是集群）和{{}的单个索引1}}和u_billhistory.UserId。

以下是重构此查询的初步尝试：

u_billhistory.PaidDate

请注意，它并不完整，因为我们没有关于您的架构和数据的所有信息，并且因为似乎缺少SELECT ub.*, u.username, u.first_name, u.last_name, u.phone, u.email, u.active, m.PaidAmount, m.PaymentMedia, m.TransactionId, y.TotalPaids, p.PopName As PopFullName, cpt2.CPRate FROM u_bills ub INNER JOIN users u on u.id = ub.UserId INNER JOIN u_setupinfos usi on usi.UserId = ub.UserID INNER JOIN pops p ON p.PopId = usi.PopName INNER JOIN ( SELECT UserId, MIN(AddedDate) As cptDate FROM cpt GROUP BY UserID ) cpt1 ON cp1.UserID = ub.UserID INNER JOIN ( SELECT UserID, AddedDate, MIN(CPRate) AS CPRate FROM cpt GROUP BY UserID, AddedDate ) cpt2 ON cpt2.UserID = ub.UserID AND cpt2.AddedDate = cpt1.ctpDate INNER JOIN ( SELECT UserID, MONTH(PaidDate) PaidMonth, SUM(PaidAmount) AS PaidAmount, PaymentMedia, TransactionId --these two fields need an aggregate function of some type! FROM u_billhistory GROUP BY UserId, MONTH(PaidDate) ) m ON m.UserID = ub.UserId AND m.PaidMonth = MONTH(ub.AddedDate) INNER JOIN ( SELECT UserID, YEAR(PaidDate) As PaidYear, GROUP_CONCAT(CONCAT(`BillHisId`,';',`PaidAmount`,';',`PaidDate`) separator '|') AS TotalPaids FROM u_billhistory WHERE YEAR(PaidDate) = YEAR(CurDate()) GROUP BY UserId, YEAR(PaidDate) ) y ON Y.UserId = ub.UserId WHERE username='abc'和两个缺少的聚合函数。 MySql这种方式很糟糕......一个更好的数据库不会允许你的查询运行，直到你修复了这些东西。

为什么这个查询花了这么长时间来执行

我在查询

1 个答案: