Princeton University Computer Science Dept.

Computer Science 425 Database Systems Andrea LaPaugh

Spring 2000

Discussion of Chapter 4, Part A: Relational Algebra

See the slides in PDF format provided by the authors of our textbook. I skipped several of the slides containing example found in the textbook specifically pages 16-19. You should review these. I added one slide on renaming (slide in PostScript) and one slide on the formal definition of the relational algebra (slide in PostScript).

We also did several examples on the board. These examples appear in the text by Silberschatz et. al., a copy of which is on reserve at the Engineering library. The most difficult example was the query: Find all customers who have accounts at all branches in Princeton. This query uses division. One correct query (from Silberschatz et. al. ) is:

PROJECT on name and bname ( depositor NATURAL JOIN acct )

DIVIDED BY

PROJECT on bname ( SELECT on bcity=Princeton (branch) )

• acct = (bname, acct#, bal)
• depositor = (name, acct#)
• branch = (bname, bcity, assets)