# DBMS/Query Languages

< DBMS

## Query Languages[edit | edit source]

- 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[edit | edit source]

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

- operations

BY:NA

### Tuple relational calculus[edit | edit source]

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.