(I realize that my title is poor. If after reading the question you have an improvement in mind, please either edit it or tell me and I'll change it.)

I have the relatively common scenario of a job table which has 1 row for some thing that needs to be done. For example, it could be a list of emails to be sent. The table looks something like this:

ID    Completed    TimeCompleted   anything else...
----  ---------    -------------   ----------------
1     No                           blabla
2     No                           blabla
3     Yes          01:04:22
...

I'm looking either for a standard practice/pattern (or code - C#/SQL Server preferred) for periodically "scanning" (I use the term "scanning" very loosely) this table, finding the not-completed items, doing the action and then marking them completed once done successfully.

In addition to the basic process for accomplishing the above, I'm considering the following requirements:

• I'd like some means of "scaling linearly", e.g. running multiple "worker processes" simultaneously or threading or whatever. (Just a specific technical thought - I'm assuming that as a result of this requirement, I need some method of marking an item as "in progress" to avoid attempting the action multiple times.)
• Each item in the table should only be executed once.

Some other thoughts:

• I'm not particularly concerned with the implementation being done in the database (e.g. in T-SQL or PL/SQL code) vs. some external program code (e.g. a standalone executable or some action triggered by a web page) which is executed against the database
• Whether the "doing the action" part is done synchronously or asynchronously is not something I'm considering as part of this question.