[2] Garcia-Molina, Ullman and Widom, Database Systems (the Complete Book), Chapters 2-3. This book also has a homepage.
[3] Atzeni and De Antonellis, Relational Database Theory. This book is on reserve in the Engineering Library.
There will also be lecture notes appearing from time to time.
[4] E.F. Codd, A Relational Model
of Data for Large Shared Data Banks,
CACM 13(6), 1970.
Material is taken mostly from [4], Chapters 1 and 2.
[5] Lecture Notes on this material will appear regularly. The first section (basics and Relational Algebra) is here. The next section (Domain and Tuple Relational Calculus) is here.
Supplemental references:
[6] Aho, A.V. and J.D. Ullman, Universality of Data Retrieval Languages,
Sixth ACM POPL, 1979.
The appendix contains the original proof that Relational Algebra (hence Relational Calculus)
cannot express transitive closure.
[7] Chandra, A.K. and D. Harel, Computable Queries for Relational Databases,
JCSS 21 (1980).
A (rather dense) discussion of completeness of query languages,
presenting a language (QL) that is shown to be complete.
[2] Chapter 10 discusses logical query languages which can express recursion.