Relational equivalence of SQL algebra "NOT IN"

Question

Is there an equivalent to relational algebra SQL expressions NOT IN?

For example, if I have a relationship:

A1  |  A2
----------
x   |  y
a   |  b
y   |  x

I want to delete all tuples in a relation for which A1 is in A2. In SQL, I can query:

SELECT
    *
FROM
    R
WHERE
    R.A1 NOT IN
        (
        SELECT
            A2
        FROM
            R
        )
/

What really throws me away is like a subquery inside a relational algebra select statement, is this possible ?:

σ _{some subquery here} R

+5

jsj Sep 22 '12 at 7:27

2 answers

. :

SQL R WHERE ... [NOT] IN S?

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: , () JOIN, bowtie ⋈.

, , SQL-. , A1 NOT IN A2. . SQL NOT where. SQL :

SELECT * FROM R
WHERE NOT (A1 IN (SELECT A2 AS A1 FROM R) )

. ( NOT MINUS .) , RA :

R - (R ⋈ ρ < > A1/A2 > (π < > 2 > (R)))

, D:

R MINUS (R JOIN (R {A2} RENAME A2 AS A1))

SQL. SQL WHERE . contra Codd 7, set-at-time.

SQL WHERE RA σ (Natural) JOIN set-at-time. (, , Date Darwen A .)

+2

AntC 02 . '13 22:29

Andomar · Accepted Answer · 2012-09-22T07:33:01+0000

In relational algebra, you can do this using a card product. Sort of:

R - p _{a1, a2} (π _{a11, a21} (σ _{A11 = A22} (ρ _{a11, a21} (R) x ρ _{a12, a22} (R))))

, . R, , .