What does left outer join mean???

[request]

I have an existing crystal report where there is a left outer join for 2 tables.
What is left outer join mean??

e.g. I have table invoice and invoice_item and they are linked as follows:

invoice.inv_no -> invoice_item.inv_no

and the type of link defined for these 2 tables is left outer join.

What does this mean?

Thanks a lot.

 

[konad]

your first table "left" will return back everything regardless of what is in the outer tables met the criteria or not