Motivating Example

• Cost: 1000 + 1000 * 500 I/Os

• By no means the worst plan!

• Misses several opportunities: selections could have been `pushed’ earlier, no use is made of any available indexes, etc.

• Goal of optimization: To find more efficient plans that compute the same answer.

SELECT S.sname

FROM Reserves R, Sailors S

WHERE R.sid=S.sid AND

R.bid=100 AND S.ratingɱ

RA Tree:

Plan:

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