[dba-SQLServer] Where does it go?

I have code which mistakenly allowed me to start a query multiple times.  Since fixed.  However that 
does raise the question... what happens inside sql server when this occurs.

the code in question was updating a specific field to null when that field was equal to ' ' (space). 
  IOW I am cycling through a bunch of fields where I have ' ' representing no value, to get a 
consistent null to represent no value.

What happens inside SQL Server if I start this same query multiple times on the same field?  I use a 
command object to start the query running.  I assume that if I were to set that command object to 
null back in C#, SQL Server is running the query and continues merrily on its way?

So if i do this three times it???  Runs that same query three times?  Sequentially (end to end?). 
Consecutively (simultaneously)?

Is there something in SQL Server I can go to see processes or threads that are running and see the 
sql statement that represents the process?  To see what SQL Statements are currently executing?

-- 
John W. Colby
www.ColbyConsulting.com