JOINS, EXISTS or IN which is better? Few questions on SQL

Question

I have few questions on SQL..

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

2. What shou

Answer 1

I guess the join gives more free to the engine for choice the best query plan. In your exactly case, probably have all solutions similar performances.

SELECT enquiry_courses.* 
FROM enquiry_courses 
INNER JOIN enquiries ON enquiries.enquiry_id=enquiry_courses 
                        AND session_id = '4cd3420a16dbd61c6af58f6199ac00f1' 

Answer 2

MSSQL generally comes with a built in gui tool called Query Analyser which describes how the query will be executed.

For 2) you could rewrite as:

SELECT * 
FROM enquiry_courses ec 
WHERE EXISTS (select 1 FROM enquiries e 
              WHERE e.enquiry_id = ec.enquiry_id 
              and e.session_id ='4cd3420a16dbd61c6af58f6199ac00f1' )

but I can't believe it would make any performance difference in a modern RDBMS.