Today's SQL Server tip

UPDATE STATISTICS v7.0
When a user comes to you and says, "My query is executing slowly," the 
first tool to pull out of your performance tuning kit is UPDATE 
STATISTICS.

When you update statistics on a table/index, you are actually telling 
SQL Server to read the data in the table and evaluate the statistical 
distribution of the key values of that data. The statistical data SQL 
Server creates resides on the distribution page of the index on the 
table. The distribution page is employed by the SQL optimizer to 
determine the best usage for a particular query.

You can issue this SQL statement with these options:

1. UPDATE STATISTICS TableX: This will update all of the index 
statistics on TableX.

2. UPDATE STATISTICS TableX idx1: This will update only the idx1 index 
statistics on TableX.

This is not a catch-all method for query tuning, but it is most likely 
your first step in attempting to troubleshoot queries that are having 
excessively slow run times. Many other factors are involved with query 
troubleshooting. No indexing and inefficient query writing are probably 
the most prevalent problems within your environment. Nevertheless, 
UPDATE STATISTICS can help.

There are additional STATISTICS options you can specify, but these are 
used in conjunction with the CREATE STATISTICS command. See MSDN Books 
Online for additional information regarding the CREATE command.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/startsql/getstart_4fht.asp