DBMS/Query Languages

Query Languages query the retrieval of tuples from the relations of a relational schema query language a language used to retrieve information (tuples) from the relations of a relational schema. types of query language procedural language non-procedural language Mathematical query languages Relational algebra Tuple relational calculus Domain relational calculus Relational algebra relational algebra is a procedural query language operations selection (r σ s) - projection (r ∏ s) - union: (r ∪ s) set difference: (r – s) Cartesian product: (r X s) rename: ( ρr ) intersection: natural join: division: union: intersection: outer join BY:NA Tuple relational calculus A tuple variable is variable that takes on tuples of a particular relation schema as values. That is, every value assigned to a given tuple variable has the same number and type of fields. A tuple relation calculus query has the form {T I p(t)} where T is a tuple variable and p(T) denotes a formula that describes T; The result of this query is the set of all tuples t for which the formula p(T)evaluates to true with T=t. Domain relational calculus