改善SQL查询选择性能

Question

我有一个SQL查询，可从多个表中提取数据。我唯一遇到的问题实际上是查询花费了很长时间，我想知道是否仍然可以加快查询速度。我通过使用INNER JOIN而不是LEFT JOIN进行了一些小的改进，但是查询速度很慢。

SELECT 
    clientlist.CRMContactId,
    clientlist.ClientAdviser,
    COALESCE(NULLIF(clientlist.FirstName, ""), clientlist.CorporateName) AS FirstName,
    clientlist.LastName,
    clientlist.ServiceStatusName, 
    FORMAT(t.totalfum, 2) AS "Funds Under Management",
    FORMAT(d.totalfci, 2) AS "Total Income", 
    (SELECT DueDate 
     FROM tasks 
     WHERE ClientRef = clientlist.ClientRef 
       AND `Status` <> "Complete" 
     ORDER BY DueDate DESC 
     LIMIT 1) AS NextDate, 
    (SELECT CompletedDate 
     FROM tasks 
     WHERE ClientRef = clientlist.ClientRef 
       AND `Status` = "Complete" 
     ORDER BY DueDate DESC 
     LIMIT 1) AS LastDate 
FROM 
    clientlist
INNER JOIN 
    (SELECT 
         plans.ClientId, SUM(plans.CurrentVal) AS totalfum
     FROM 
         plans
     GROUP BY 
         plans.ClientId) t ON clientlist.CRMContactId = t.ClientId
INNER JOIN 
    (SELECT 
         adviserfci.ClientId, SUM(adviserfci.Payable) AS totalfci
     FROM 
         adviserfci
     WHERE 
         IncomeType IN ("Renewal Commission", "Ongoing Fee", "Fund Based Commission") 
         OR (Incometype = "Payaway Received" 
             AND UnderlyingIncomeType IN ("Renewal", "Ongoing Fee", "Fund Based"))
     GROUP BY 
         adviserfci.ClientId) d ON clientlist.CRMContactId = d.ClientId
WHERE 
    d.totalfci IS NOT NULL

我还在某处阅读了explain命令，它将帮助您确定问题，但是我不理解响应。

有什么办法可以提高此查询的性能？

Answer 1

首先要为这些表创建索引吗？

不知道您的数据结构和要放入哪种查询负载很难说，但是乍一看，我想说这些索引应该提高性能，如果还没有的话：

• 表clientlist上的CRMContactId
• 餐桌上的ClientId
• advisrfci上的ClientId（包括IncomeType和Payable）

如果您尚未设置表主键，并且从列名称中听起来像是不错的候选键，那么如果可行，您可以用一块石头杀死两只鸟。

Answer 2

将d.totalfci IS NOT NULL的测试折叠到生成它的子查询中，即使它需要放在HAVING子句中。

添加一些索引

tasks:  INDEX(ClientRef, `Status`, DueDate)
plans:  INDEX(ClientId, CurrentVal)
adviserfci:  INDEX(ClientId)