how to optimize sql query

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Which one is faster? Join or Subquery?

Posted 11-Oct-15 18:38pm

Mir Mohammad Nur-E-Alam

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Maciej Los · Answer 1 · 2015-10-11T20:00:00

Solution 1

It depends on many factors. Please, see past answers and CP Knowledge Base articles[^].

Posted 11-Oct-15 20:00pm

Maciej Los

jgakenhe · Answer 2 · 2015-11-25T16:39:00

There is no clear cut answer. Typically in SQL Server you would you JOINs, but in Oracle you'd use Subqueries. The each DBMS is designed to optimize that way, but it isn't always true. Here are a couple of nice examples on how to use the SQL Server Execution Plan to test performance of JOINs and Subqueries; if you've never used that.

http://blog.sqlauthority.com/2010/06/06/sql-server-subquery-or-join-various-options-sql-server-engine-knows-the-best/[^]

http://sqlstudies.com/2013/05/02/comparing-an-inner-join-vs-a-subquery/[^]

Magic Wonder · Answer 3 · 2015-10-11T20:54:00

Solution 2

Hi,

Check this...

Joins Vs Subqueries[^]

Hope this will help you.

Cheers

Posted 11-Oct-15 20:54pm

Magic Wonder

Jörgen Andersson · Answer 4 · 2015-11-25T23:19:00

Joins and subqueries are semantically different and may give different results.
For those cases when they are equivalent the optimizer on all modern RDBs will know that and convert subqueries to joins where it gives a better result.

So the answer is, use the query that gives the right result.

how to optimize sql query

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