Can the community suggest some T-SQL practice/sample exams, and tips on increasing performance/tuning? This is for preparing interview. Thanks.
An SO search for interview+questions+sql
To be brutal, you can't learn answers to questions they may ask. Either you know or you don't. It's easily spotted if they hire consultants too (I was interviewed by a famous MS bloke once, had a book or 2 of his on my desk) because they don't yet have in house skills.
T-SQL 'exams' are tough to come by. There are a lot of concepts that you can't really grasp until you've used them (and usually after some very painful hours working on "weird" issues).
Depending on how advanced you're looking to get, if you'd like to really go nuts and see what you're capable of, look at http://beyondrelational.com/tc/ There are challenges that people compete in. If you're looking for more of a try/learn approach, do an older challenge and peek at the answer if you can't quite figure it out.
Actually, looking at the page now I see that they have beginner challenges as well.