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how sql doing inner join

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harshiloh
Starting Member

1 Posts

Posted - 05/03/2012 : 07:52:09

1.)please explain the algorithm of sql inner join,

2.)
User table (20 core user)
ID,Name,CityId

City table (1 lakh city)
Id,Name,CountryId

select * from User inner join City on User.CityId=City.Id
select * from City inner join User on User.CityId=City.Id

which one is better ?why?

robvolk
Most Valuable Yak

USA
15559 Posts

Posted - 05/03/2012 : 09:17:39

1. There are 3 types, nested loops, merge, and hash joins. More info on them here:

http://www.sql-server-performance.com/2010/pysical-join-operators/
http://msdn.microsoft.com/en-us/library/ms173815.aspx

2. Neither one is better, they're exactly the same query and will return the same results.