Question

clef name opus_num key Writes Composer Piece score 0 Orchestral Playsln Instrument quantity lyrics

Write relational algebra expressions to retrieve the following information from the music database. Use the most appropriate operations for each query. In particular, use joins when appropriate.

(a) For each composer, give the composer’s name and the total number of pieces that (s)he has written, including composers who have not written any pieces.

(b) For each type of instrument, give the instrument type together with the total number of orchestral pieces which use that type of instrument.

Answer 1

a)

$\pi$_{name, name g count(pous_num)} ( Composer $\Join$ Piece)

b)

$\pi$_{type, type g count(pous_num)} ( Instrument $\Join$ Orchestral )

$\pi$ --- projection operation

$\Join$ ---- join

g is group by

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