select from the same table twice using aliases

Please start any new threads on our new site at https://forums.sqlteam.com. We've got lots of great SQL Server experts to answer whatever question you can come up with.

All Forums

General SQL Server Forums

New to SQL Server Programming

select from the same table twice using aliases

Author

Topic

alex100
Starting Member

5 Posts

Posted - 2010-09-18 : 07:30:39

Hi,

when i select from the same table twice(using alases), I get more records than i expected.

why does it occures ?

Regards,
Alex

this is my table -
column_ID
1
2
3

after executing the following query

select T1.column_ID
from table_1 as T1, table_1 as T2

i get those results :
column_ID
1
2
3
1
2
3
1
2
3

webfred
Master Smack Fu Yak Hacker

8781 Posts

Posted - 2010-09-18 : 07:34:45

You are joining without any condition so each possible pair is created.
It is a cartesian product.
http://en.wikipedia.org/wiki/Cartesian_product

No, you're never too old to Yak'n'Roll if you're too young to die.