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Whats the difference between an INNER JOIN and a WHERE clause

Posted on 2014-10-11
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Last Modified: 2014-10-17
If I have
From
table Sales A
INNER JOIN table Salespeople B
ON
A.SalesID = B.SalesID

Then what are the pro/cons of doing the below instead
table Sales A, table SalespeopleB
Where
A.SalesID = B.SalesID
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Question by:upobDaPlaya
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7 Comments
 
LVL 21

Expert Comment

by:pinaldave
ID: 40375539
For inner join there is no difference if you put condition in where or join statement.

It differs for outer join.
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Accepted Solution

by:
Éric Moreau earned 1000 total points
ID: 40375638
a where clause is to filter out rows that you don't need.

Join is used to get data from other tables.

if you use a INNER join, that means that the link to the second must return data in order for the data of the first table to be returned.

a LEFT (or RIGHT) join does not filter out.
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Author Comment

by:upobDaPlaya
ID: 40375703
Which is more efficient...
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Expert Comment

by:Éric Moreau
ID: 40375748
they are different. If you can avoid going to the second table, it will be more efficient but sometimes you don't have all the data in the first table to filter out unwanted rows
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LVL 21

Assisted Solution

by:pinaldave
pinaldave earned 1000 total points
ID: 40375828
Both will give you the same performance in the case of SQL Server when you use INNER JOIN.
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LVL 70

Expert Comment

by:Éric Moreau
ID: 40375836
I looked back at your 2 queries. The second one is using the old syntax.

As said by pinaldave, in this very specific case, both queries will perform exactly the same. If you check the Execution plan for both queries (from SSMS), you would find that the SQL engine transforms the second query in the same format as the first one.
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Author Closing Comment

by:upobDaPlaya
ID: 40387969
Thanks was always wondering on the above so thanks for answering
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