Physical Operators

Question

Physical Operators

ramana3327

SSCoach

Points: 19700
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December 25, 2013 at 8:37 am

#286503

Hi what is the main difference b/n mergejoin, hash join & nested loop join? In which cases those will form? Please tell me which is the very bad performance issue. i.e. most costly operator.

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Jeff Moden SSC Guru Points: 1003863 More actions · Answer 1

ramana3327 (12/25/2013)
Hi what is the main difference b/n mergejoin, hash join & nested loop join? In which cases those will form? Please tell me which is the very bad performance issue. i.e. most costly operator.

Looking at your other posts and to be honest, you're asking a whole lot of questions where the answers are easily found in "Books Online". For example, if you search for "Merge Join" in "Books Online", not only will you find something that tells you what it is, but you'll also get some hints as to when such a join could be a performance problem. Here's the last sentence in that entry.

Merge join itself is very fast, but it can be an expensive choice if sort operations are required. However, if the data volume is large and the desired data can be obtained presorted from existing B-tree indexes, merge join is often the fastest available join algorithm.

If you don't specifically know what "Books Online" actually is, open SSMS, press the {f1} key, and you're there. I strongly recommend that you spend some time looking for the answers to your questions there so that you become more familiar with the tool especially since it's usually much quicker to find your own information than it is to post to a forum.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 2

ramana3327 (12/25/2013)
Please tell me which is the very bad performance issue.

All of them. None of them.

If there was a join operator that always was a performance problem, why would SQL use it?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

SQLRNNR SSC Guru Points: 281334 More actions · Answer 3

This reads like somebody is prepping for an interview or somebody just finished an interview.

Gail's answer is entirely accurate. Hang around a bit on the forums and explore some execution plans and you will start to see why.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
Posting Performance Based Questions - Gail Shaw[/url]
Learn Extended Events

ramana3327 SSCoach Points: 19700 More actions · Answer 4

Some are confusing to me. I want to hear from experience guys like you.