Query Languages

nLanguage in which user requests information from the database.

nCategories of languages

lProcedural

lNon-procedural, or declarative

n“Pure” languages:

lRelational algebra

lTuple relational calculus

lDomain relational calculus

nPure languages form underlying basis of query languages that people use.

Relational Algebra

nProcedural language

nSix basic operators

lselect: s

lproject: Õ

lunion: È

lset difference: –

lCartesian product: x

lrename: r

nThe operators take one or  two relations as inputs and produce a new relation as a result.