rename

In relational algebra, a rename is a unary operation written as




ρ

a

/

b


(
R
)


{\displaystyle \rho _{a/b}(R)}
where:

R is a relation
a and b are attribute names
b is an attribute of RThe 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:

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





ρ

a

/

b


(
R
)
=
{

t
[
a

/

b
]
:
t
∈
R

}


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



t
[
a

/

b
]


{\displaystyle 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
)
∈
t
,

c
≠
b

}
∪
{

(
a
,

t
(
b
)
)

}


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

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