In relational algebra, a rename is a unary operation written as
ρ
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
E
m
p
l
o
y
e
e
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
}
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
)
∈
t
,
c
≠
b
}
∪
{
(
a
,
t
(
b
)
)
}
