Simple Selections

• Of the form

• 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.)

• Result size estimation:

(Size of R) * reduction factor.

More on this later.

SELECT *

FROM Person R

WHERE R.phone < ‘543%’

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