When you do a non updating update like the one below
SET i = 1
In SQL 2000, the lack of the optimization leads to updating the nonclustered index even if the value is not changing.
In the SQL 2005 plan, it is possible to appreciate
- a “Compute Scalar” operator that compares the current value and new value of the column being modified
- a new filter operator that on a row by row basis will determine whether the nonclustered index is being affected or not
- the fact that nonclustered index maintenance is now bypassed
Read the whole article (including statistics profile output screenshot) at the Tips, Tricks, and Advice from the SQL Server Query Optimization Team blog