Rename (relational algebra)

In relational algebra, a rename is a unary operation written as $\rho _{a/b}(R)$ where:

$R$ is a relation
$a$ and $b$ are attribute names
$b$ is an attribute of $R$

The result is identical to $R$ except that the $b$ attribute in all tuples is renamed to $a$ . For an example, consider the following invocation of $ρ$ on an $Employee$ relation and the result of that invocation:

{\text{Employee}}

\rho _{\text{EmployeeName/Name}}({\text{Employee}})

Name	EmployeeId
Harry	3415
Sally	2241

EmployeeName	EmployeeId
Harry	3415
Sally	2241

Formally, the semantics of the rename operator is defined as follows:

\rho _{a/b}(R)=\{\ t[a/b]:t\in R\ \}

where $t[a/b]$ is defined as the tuple $t$ , with the $b$ attribute renamed to $a$ , so that:

t[a/b]=\{\ (c,v)\ |\ (c,v)\in t,\ c\neq b\ \}\cup \{\ (a,\ t(b))\ \}