尝试优化查询性能（MySQL）

Question

所以我有一张有很多外键的表，但是当我要记录时，我需要加入这些表上的所有内容，因为我通常需要这些字段才能使记录有意义。基本查询如下所示：

SELECT i.id, i.`key`, i.title, i.description,
CONCAT(ru.firstName, ' ', ru.lastName) as `name`,
CONCAT(au.firstName, ' ', au.lastName) as `name`,
p.title, pc.title, pva.title, pvo.title, pvf.title, i.durationEstimate,
i.storyPoints, i.dueDate, isl.title, i.rejectionCount,
CONCAT(uc.firstName, ' ', uc.lastName) as `name`,
i.createdTimestamp, i.updatedTimestamp, it.title, isss.title
FROM ProjectManagement2.Issues i
INNER JOIN Users ru ON ru.id = i.reporterUserUsername
INNER JOIN Users au ON au.id = i.assignedUserUsername
INNER JOIN Projects p ON p.id = i.projectTitle
INNER JOIN ProjectComponents pc ON pc.id = i.projectComponentTitle
INNER JOIN ProjectVersions pva ON pva.id = i.affectedProjectVersionTitle
INNER JOIN ProjectVersions pvo ON pvo.id = i.originalFixedProjectVersionTitle
INNER JOIN ProjectVersions pvf ON pvf.id = i.fixedProjectVersionTitle
INNER JOIN IssueSecurityLevels isl ON isl.id = i.issueSecurityLevelId
INNER JOIN IssueTypes it ON it.id = i.issueTypeId
INNER JOIN IssueStatuses isss ON isss.id = i.issueStatusId
INNER JOIN Users uc ON uc.id = i.creatorUserUsername
LIMIT 50000, 100;

这个查询在我第一次运行后大约需要 880 毫秒才能运行（需要几秒钟）。此查询的 EXPLAIN 显示：

1   SIMPLE  pvo index   PRIMARY title   98  NULL    22  Using index
1   SIMPLE  i   ref     reporterUserUsername,assignedUserUsername,projectTitle,projectComponentTitle,affectProjectVersionTitle,originalFixedProjectVersionTitle,fixedProjectVersionTitle,issueSecurityLevelId,creatorUserUsername,issueTypeId,issueStatusId 
       originalFixedProjectVersionTitle 5   ProjectManagement2.pvo.id   1136    Using where
1   SIMPLE  isl ALL     PRIMARY NULL    NULL    NULL    5   Using where; Using join buffer
1   SIMPLE  isss eq_ref PRIMARY PRIMARY 4   ProjectManagement2.i.issueStatusId  1   
1   SIMPLE  pc  eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.projectComponentTitle  1   
1   SIMPLE  pva eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.affectedProjectVersionTitle    1   
1   SIMPLE  p   eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.projectTitle   1   
1   SIMPLE  pvf eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.fixedProjectVersionTitle   1   
1   SIMPLE  ru  eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.reporterUserUsername   1   
1   SIMPLE  au  eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.assignedUserUsername   1   
1   SIMPLE  uc  eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.creatorUserUsername    1   
1   SIMPLE  it  eq_ref  PRIMARY PRIMARY 4   ProjectManagement2.i.issueTypeId

最大的问题是当我向查询添加订单时，在第一次查询后需要几秒钟。

我可以做些什么来优化此查询（如果您需要更多信息，请告诉我）？

Answer 1

您的原始查询将所有内容连接在一起，然后在显示接下来的 100 行之前将 50000 行遍历到连接数据中。尝试这个

• 预先从 ProjectManagement2 获取 100 个密钥
• 之后加入一切

这是我建议的查询

SELECT i.id, i.`key`, i.title, i.description,
CONCAT(ru.firstName, ' ', ru.lastName) as `name`,
CONCAT(au.firstName, ' ', au.lastName) as `name`,
p.title, pc.title, pva.title, pvo.title, pvf.title, i.durationEstimate,
i.storyPoints, i.dueDate, isl.title, i.rejectionCount,
CONCAT(uc.firstName, ' ', uc.lastName) as `name`,
i.createdTimestamp, i.updatedTimestamp, it.title, isss.title
FROM
(
    SELECT B.* FROM
    (SELECT id FROM ProjectManagement2 LIMIT 50000, 100) A
    INNER JOIN ProjectManagement2 B USING (id)
) i
INNER JOIN Users ru ON ru.id = i.reporterUserUsername
INNER JOIN Users au ON au.id = i.assignedUserUsername
INNER JOIN Projects p ON p.id = i.projectTitle
INNER JOIN ProjectComponents pc ON pc.id = i.projectComponentTitle
INNER JOIN ProjectVersions pva ON pva.id = i.affectedProjectVersionTitle
INNER JOIN ProjectVersions pvo ON pvo.id = i.originalFixedProjectVersionTitle
INNER JOIN ProjectVersions pvf ON pvf.id = i.fixedProjectVersionTitle
INNER JOIN IssueSecurityLevels isl ON isl.id = i.issueSecurityLevelId
INNER JOIN IssueTypes it ON it.id = i.issueTypeId
INNER JOIN IssueStatuses isss ON isss.id = i.issueStatusId
INNER JOIN Users uc ON uc.id = i.creatorUserUsername
;

试一试 ！！！