From SqlMyopia, on the topic of relational calculus & algebra:
My favorite book to cover all of these topics is FundamentalsOfDatabaseSystems by Elmasri and Navathe. It covers the math, as well as SQL. -- KyleBrown
FundamentalsOfDatabaseSystems by RamezElmasri? and ShamkantNavathe?, Addison-Wesley, 1999 (3rd ed.), ISBN 0805317554
Why are database reference books often close to 1000 pages? The topic has a well-formed theoretical basis (compared to Operating Systems, say) and very well-understood role. It should be possible to distill this into something more like KernighanAndRitchie or Iverson's book on AplLanguage or Allen's Probability, Statistics, and Queueing theory (talk about covering a lot in a short, readable book). If I were to deconstruct most DB tomes I would conclude
(A) authors have an inferiority complex about their field (B) authors condescend to their readers (O'Reilly T-SQL book is an example)