title: Performance implications of computed columns in SQL Server 2005 database?
body: <p>The situation: we have a large database with a number of denormalized tables. We frequently have to resummarize the data to keep the summary tables in synch. We've talked on and off about using computed columns to keep the data fresh. We've also talked about triggers, but that's a separate discussion.</p>
  
  <p>In our summary tables, we denormalized the table such that the Standard ID as well as the Standard Description is stored in the table.  This inherently assumes that the table will be resummarized often enough so that if they change the standard description, it will also change it in the summary table.
  A bad assumption.</p>
  
  <p>Question:
  What if we made the Standard Description in the summary table a derived/computed column which selects the standard description from the standard table?
  Is there a tremendous performance hit by dropping a computed column on a table with 100,000-500,000 rows?</p>