If an index is fragmented, how does the optimizer respond on this? In other words: how does the optimizer decide not to use an index because of its fagmentation? If statistics are outdated, is this also a reason not to use the index, or is the optimizer in that case just using outdated data? Let's say you don't rebuild your indexes but only update your statistics. Is there a point when SQL decides not to use the indexes (because of a high fragmentation) regardless of the actual statistics?