how to lock a table or row in sql?

hi, i have an application that updates some records in sql tables, and i want to do a web application that updates records in the some database-table(sql) so, my question is how can i lock the row or table so i dont have concurrency problems.
tnx in advance.Have you tried google? Search fordatabase concurrency.
It's not a simple answer. There are different types of concerrency and different levels of locks. You need to undestand what is out there. Once you get the difference, you'll probably know what to use and how to do it.
Now go. Google it.|||

ok , i will try doing something like in this article..

http://www.15seconds.com/issue/030604.htm

tnx Alex.