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A question suddenly came to my mind while I was tuning one stored procedure. Let me ask it -

I have two tables, table1 and table2. table1 contains huge data and table2 contains less data. Is there performance-wise any difference between these two queries(I am changing order of the tables)?

Query1:

SELECT t1.col1, t2.col2
FROM table1 t1
INNER JOIN table2 t2
ON t1.col1=t2.col2

Query2:

SELECT t1.col1, t2.col2
FROM table2 t2
INNER JOIN table1 t1
ON t1.col1=t2.col2

We are using Microsoft SQL server 2005.

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1 Answer

Aliases, and the order of the tables in the join (assuming it's INNER JOIN) doesn't affect the final outcome and thus doesn't affect performance since the order is replace (if needed) when the query is executed.

You can read some more basic concepts about relational algebra here: http://en.wikipedia.org/wiki/Relational_algebra#Joins_and_join-like_operators


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