如何优化SQL查询？ [英] How to optimize SQL query ?

问题描述

我有3张如下表格

I have 3 tables like below

Student 
   	stdId
	stdName
        stdCourseID
StudentCources
        stdCourseID
        courseName
        stdeventID
StudentEvents
        stdeventID
        eventName

i想要填写所有这些属性，如下所示

i want to fill all these properties like below

stdId
stdName

stdCourseName

stdEventName

当我尝试使用此查询时，我将获得重复的stdId，stdName和stdCourseID，以及重新生成项目列表中的corseName和eventName

when i try with this query i am getting duplicate stdId , stdName and stdCourseID follewd by list of remaning items corseName and eventName

select * from Student as s WITH(NOLOCK) 
join StudentCources as se WITH(NOLOCK) on sc.stdCourseID = s.stdCourseID 
join StudentEvents as se WITH(NOLOCK) on se.stdeventID = se.stdeventID  
where s.stdId=118

我尝试过：

What I have tried:

select name,courseName,eventName from Student as s WITH(NOLOCK) 
join StudentCources as se WITH(NOLOCK) on sc.stdCourseID = s.stdCourseID 
join StudentEvents as se WITH(NOLOCK) on se.stdeventID = se.stdeventID  
where s.stdId=118

你能告诉我如何优化这个应该获取所有数据的查询

Could you please tell me how to optimize this query that should fetch all data

推荐答案

另外，如果你的学生没有在StudentCources[sic]表和StudentEvents表中有一条记录，它将返回一个空集，因为你使用的是隐含的INNER JOIN。

Also, if your student doesn't have a record in either the "StudentCources" [sic] table and "StudentEvents" table, it will return an empty set because you are using an implied INNER JOIN.

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