JOINS、EXISTS 或 IN 哪个更好?关于SQL的几个问题 [英] JOINS, EXISTS or IN which is better? Few questions on SQL

问题描述

我有几个关于 SQL 的问题..

I have few questions on SQL..

1. 如何分析一个系统的性能询问?任何软件，内置MSSQL Server 2005/2008 的特点?

1. How to analyze the performance of a query? Any software, inbuilt features of MSSQL server 2005/2008?

在查询中应该用什么代替in才能使性能更好?例如:

What should be used in place of inin queries so that the performance is better? Eg:

选择 *FROM enquiry_courses在哪里enquiry_id IN( SELECT enquiry_id FROM 查询 WHERE session_id = '4cd3420a16dbd61c6af58f6199ac00f1' )

SELECT * FROM enquiry_courses WHERE enquiry_id IN ( SELECT enquiry_id FROM enquiries WHERE session_id = '4cd3420a16dbd61c6af58f6199ac00f1' )

在性能方面，JOINS、EXISTS 或 IN 哪个更好?

Which is better: JOINS, EXISTS or IN in terms of performance?

感谢评论/帮助...

推荐答案

1. 使用 SQL Server Management Studio，并包括 Actual Execution Plan 和 SET STATISTICS TIME 和 SET STATISTICS IO.

这对应于 JOIN，但重写可能无关紧要.猜测可能是您需要 enquiry_courses.enquiry_id 和 enquiries.session_id 上的索引来提高查询性能.

This in corresponds to a JOIN, but rewriting probably won't matter. A guess could be that you need indexes on enquiry_courses.enquiry_id and on enquiries.session_id to improve query performance.

这篇关于JOINS、EXISTS 或 IN 哪个更好?关于SQL的几个问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！