CODEWITHSUNDEEP
sqlsql-serversql-server-2005performancet-sql
Mutation Person
Mutation Person

Reputation: 30498

Can an INNER JOIN offer better performance than EXISTS

I've been investigating making performance improvements on a series of procedures, and recently a colleague mentioned that he had achieved significant performance improvements when utilising an INNER JOIN in place of EXISTS.

As part of the investigation as to why this might be I thought I would ask the question here.

So:

And really, any other experience people can bring to bear on this question.

I would appreciate if any answers could address this question specifically without any suggestion of other possible performance improvements. We've had quite a degree of success already, and I was just interested in this one item.

Any help would be much appreciated.

Upvotes: 78

Views: 72065

Answers (3)

Roma Ruzich
Roma Ruzich

Reputation: 752

In sql server 2019 queries with IN, EXIST, JOIN statements have different plans (if correct indexes added). So performence also is different. It is shown in article https://www.mssqltips.com/sqlservertip/6659/sql-exists-vs-in-vs-join-performance-comparison/ that JOIN is some faster.

P.S. I understand that question was about sql server 2005 (in tags), but people mostly looks for answer by article title.

Upvotes: 2

Quassnoi
Quassnoi

Reputation: 425341

Generally speaking, INNER JOIN and EXISTS are different things.

The former returns duplicates and columns from both tables, the latter returns one record and, being a predicate, returns records from only one table.

If you do an inner join on a UNIQUE column, they exhibit same performance.

If you do an inner join on a recordset with DISTINCT applied (to get rid of the duplicates), EXISTS is usually faster.

IN and EXISTS clauses (with an equijoin correlation) usually employ one of the several SEMI JOIN algorithms which are usually more efficient than a DISTINCT on one of the tables.

See this article in my blog:

Upvotes: 80

gbn
gbn

Reputation: 432220

Maybe, maybe not.

  • The same plan will be generated most likely
  • An INNER JOIN may require a DISTINCT to get the same output
  • EXISTS deals with NULL

Upvotes: 16

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