I'm not the expert on indexes really - I'm trying to work my way through a few materials now.
Anyway, let's say I have a table with 7 million records spanning 3 years. However the most common query will pull say the last 3 months -- using an integer field (unix epoch time).
This 3 month query usually takes about 18 seconds --- but many other queries may be built atop it, so I was trying to speed it up. I created a clustered index on the unix_epoch_time int field that would eventually be in a 'where' statement filter.
However, this doesn't appear to have sped up the query time at all. Does this mean this clustered index is a spurious waste? Or accounts for something like 1% of the query time? I thought it would be much faster.