Relational Algebra
 So far we have considered how to structure data using the relational model.
 We need a language to answer questions — queries — about the data.
 SQL is that language.
 Before we get to SQL, it is important to learn Relational Algebra.
 is the basis of SQL semantics,
 And of query optimization techniques which are essential to making SQL practical.
Algebra
 An is a set of operations on values of
some type, which yield values of the same type.
 E.g. +, −, ×, and ÷ are operations on numbers which yield numbers.
Relational Algebra
 An algebra for relations (tables).
 Setoriented: a relation is a set.
 This was a revolutionary idea in 1970, because all database languages at
the time were recordatatime.
