ScottPletcher (1/9/2013)
If SQL needs only key column(s), why does it read all the leaf pages of the table as well?? That's an incredible waste of I/O.
The only place that all the rows are stored is at the leaf level of an index. All that's at the non-leaf levels (any index, clustered or nonclustered) is the key columns for the first row on each page of the level below, hence there's no way to get at the key columns without reading the leaf level.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability