Simple Selections

Size of result approximated as size of R * reduction factor; we will consider how to estimate reduction factors later.

With no index, unsorted: Must essentially scan the whole relation; cost is M (#pages in R).

With an index on selection attribute: Use index to find qualifying data entries, then retrieve corresponding data records. (Hash index useful only for equality selections.)

SELECT *

FROM Reserves R

WHERE R.rname < ‘C%’

Of the form