SQL injection Patterns

I am studying SQL injection attacks. Generelly what patters in the incoming stream presents the occurence of SQL injection attacks. 

Thanks in advance.

Nitish

------------------------------------------------------------------------
Test Your IDS

Is your IDS deployed correctly?
Find out quickly and easily by testing it 
with real-world attacks from CORE IMPACT.
Go to http://www.coresecurity.com/index.php5?module=Form&action=impact&campaign=intro_sfw 
to learn more.
------------------------------------------------------------------------