Search Results for “rename (relational algebra)”

Source: Rename (relational algebra)

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 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:

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))\ \}.}