Relational database systems are expected to be equipped with a query language that can assist its users to query the database instances. Relational algebra is relational algebra operations in dbms pdf procedural query language, which takes instances of relations as input and yields instances of relations as output.
It uses operators to perform queries. An operator can be either unary or binary.
They accept relations as their input and yield relations as their output. Relational algebra is performed recursively on a relation and intermediate results are also considered relations. We will discuss all these operations in the following sections. It selects tuples that satisfy the given predicate from a relation.
Where σ stands for selection predicate and r stands for relation. Selects tuples from books where subject is ‘database’. Selects tuples from books where subject is ‘database’ and ‘price’ is 450. Selects tuples from books where subject is ‘database’ and ‘price’ is 450 or those books published after 2010.