If the Marks column is intended to be numerically additive, for example summed or averaged for a cumulative score, then you don't want special codes representing absent or other otherwise....

From what you've already described, this sounds like a direct SQL select. 

However, if this were a stored procedure call, then you would have more options for mitigating this...

Debates over primary keys and clustered indexes never get old.

Code compilation isn't much of an issue in my realm. However, if a user runs a query that joins two or more billion row tables using a non-indexed expression and...

... This is attributed to the user clicking the operation, waiting a bit for a response, and when one was not presented, clicking the button again. I know what...

There is no compelling reason to avoid cursors and dynamic sql when you're doing something like coding an administrative script that is occasionally used to iterate across databases or servers....

You might as well disable the login until the application is fixed.

A lot of application developers only work with transient persistence layers, something like session state for an embedded application or the shopping cart for an eCommerce website. In that case,...