Rename (relational algebra)
In relational algebra, a rename is a unary operation written as where:
The result is identical to R except that the b attribute in all tuples is renamed to a.[1] For an example, consider the following invocation of ρ on an Employee relation and the result of that invocation:
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Formally, the semantics of the rename operator is defined as follows:
![{\displaystyle \rho _{a/b}(R)=\{\ t[a/b]:t\in R\ \},}](https://wikimedia.org/api/rest_v1/media/math/render/svg/37e1c7381f30614642dc3141f99d88ae31e4b2cf)
where is defined as the tuple t, with the b attribute renamed to a, so that:
![{\displaystyle t[a/b]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/bbab11c03d9acf478fe64385f4c2de11cabec1f2)
![{\displaystyle t[a/b]=\{\ (c,v)\ |\ (c,v)\in t,\ c\neq b\ \}\cup \{\ (a,\ t(b))\ \}.}](https://wikimedia.org/api/rest_v1/media/math/render/svg/7368ba4d1ae9dd8efb981bb4a5be854c18286a1f)
References
[edit]- ^ Introduction to Database Systems. Pearson Education India. 2010. pp. 103–105. ISBN 978-81-317-3192-5.