Relational algebra is the formal language of the relational model. It defines a set of closed operations over relations, that is, the result of each operation is a new relation. Relational algebra inherits many operators from set algebra. Relational algebra operations could be categorized into two groups:

- The first one is a group of operations which are inherited from set theory such as
`UNION`

,`INTERSECTION`

,`SET DIFFERENCE`

, and`CARTESIAN PRODUCT`

, also known as`CROSS PRODUCT`

. - The second is a group of operations which are specific to the relational model such as
`SELECT`

and`PROJECT`

.

Relational algebra operations could also be classified as binary and unary operations. Primitive relational algebra operators have ultimate power of reconstructing ...

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