Language in which user requests information from the database
Relational algebra is one of the two procedural/formal query language associated with relational model.
Its is theoretical approach
Relational model consist two theoretical language (1) Relational Algebra (2) Relational Calculus
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Like any other mathematical system is defines a number of operators and use relations (tables) as operands.
In RA / RC you can’t use English Keywords.
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Operator(s) – Select
Horizontal partition – (to select few row or all)
Vertical partition – (to select few column or all)
(projection)
Can combine both partition
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Keys
Let K ⊆ R
K is a superkeyof R if values for K are sufficient to identify a unique tuple of each possible relation r(R)
by “possible r” we mean a relation r that could exist in the enterprise we are modeling.
Example: {customer-name, customer-street} and� {customer-name} �are both superkeys of Customer, if no two customers can possibly have the same name.
K is a candidate key if K is minimal�Example: {customer-name} is a candidate key for Customer, since it is a superkey (assuming no two customers can possibly have the same name), and no subset of it is a superkey.