Sql Server 2008 Update query is taking so much time

I have a table name Companies with 372370 records.

And there is only one row which has CustomerNo = 'YP20324'.

I an running following query and its taking so much time I waited 5 minutes and it was still running. I couldn’t figure out where is the problem.

UPDATE Companies SET UserDefined3 = 'Unzustellbar 13.08.2012' WHERE CustomerNo = 'YP20324'

Answer

You don’t have triggers on update on that table? Do you have a cascade foreign key based on that column?

Are you sure of the performance of your server? try to take a look of the memory, cpu first when you execute the query (for example on a 386 with 640mb i could understand it’s slow :p)

And for the locks, you can right click the database and on the report you can see the blocking transactions. Sometimes it helps for concurrent access.