Has anyone ever seen it where you do a join on two tables and the field that you're doing the join on are of different cases and it doesn't join? Both tables have a collation of latin_swedish_ci. I've tried the same query on a different server and it works fine. The server where it fails is 5.0.32 and the two servers that work are 5.0.51 and 5.0.24. Is there somewhere else that this case sensitivity could be affecting the outcome?

Use a left join and explicity denote which columns should be mapped to which columns:

SELECT * FROM t1 LEFT JOIN ( t2 )
                 ON ( t2.c = t1.c )

That is exactly how i'm doing the join. I even tried switching it to an inner join to see if that had any effect.

Are you really sure the tables both have an case insensitive collation ?

Just to verify, I took a test table, and tried to join it to itself between an user name and username.
The username was an upper() of the name, and it worked.
Maybe it's another clause of the join that prevent it from working.
Did you tried to join just on that (var)char field to see the results ?

I have looked at the create statment's for the tables and also verified it in the INFORMATION_SCHEMA database to make sure. I've taken the tables out of a bigger query and only used the two tables. The join failed and then I updated the field that was lowercase and made it upper case and the join worked. Switched it back to lower case and it failed again. I wrap the upper() around the field and it works. I've also tried joining other tables with the same collation on the same server and they work with different cases. Something is causing it, and I'm not going to stop looking until I understand why. Hopefully with your help . Thank you.