Thanks friend, SQL on AS/400 and no in SQL Server.
if you are using MS SQL 2005 <a href="http://searchsqlserver.techtarget.com/tip/0,289483,sid87_gci1127863,00.html">you can read this</a>, otherwise please be more specific and post more information on the SQL you are using.
If the user interface to SQL is through QM, then yes, you can prohibit the use of UPDATE or any other SQL statement. But if other interfaces are available, particularly STRSQL, then no, you can't.
Network interfaces can be restricted with exit programs, but it's practically impossible to enforce for actual statements due to the extreme variety of potential formats. I.e., an UPDATE doesn't have to done via a statement that begins with "UPDATE".