[cc]mc |
.hd rdint "intersect two identical relations" 07/01/82
rdint
.ds
'Rdint' is part of the toy relational data base system, 'rdb'. It
creates a new relation by performing the intersection of the two
relations specified as standard inputs 1 and 2 and writes the new
relation on standard output 1. Both relations must have identical
descriptions -- the domains must be identical and in the same order.
.sp
The intersection creates a new relation containing all the rows which
appear in both sets -- all other rows are discarded.  Identical rows are
not removed from the resulting relation.  These can be removed by using
'rdsort' and 'rduniq'.
.nf

     For example:

       p1.rel  --------------  p2.rel --------------
               |code | name |         |code | name |
               --------------         --------------
               | 100 | pens |         | 100 | pens |
               |-----|------|         |-----|------|
               | 101 | ink  |         | 105 | ruler|
               --------------         --------------

       p1.rel> p2.rel> rdint >p.rel

                     p.rel --------------
                           |code | name |
                           --------------
                           | 100 | pens |
                           --------------

.fi
.sp
The input relations must be files containing relations that were created
by 'rdmake' or other 'rdb' programs; relations cannot be read from the
terminal.  The output relation is displayed in a readable format if
standard output is directed to a terminal; otherwise, the output relation
is written in binary internal format for processing by other 'rdb'
programs.
.es
p1.rel> p2.rel> rdint >p.rel
p1.rel> p2.rel> rdint | rdsort | rduniq | rdprint
.me
"Sorry, a relation can't be read from the terminal"
.br
"relation is corrupted!!"
.br
"Can't access input relation 1"
.br
"Can't access input relation 2"
.br
"Relations must have identical descriptions"
.sa
rdcat (1),
rdextr (1),
rdjoin (1),
rdmake (1),
rdprint (1),
rdproj (1),
rdsel (1),
rdsort (1),
rduniq (1),
rdatt (1),
rdavg (1),
rdcount (1),
rddiff (1),
rddiv (1),
rdmax (1),
rdmin (1),
rdnat (1),
rdsum (1)
[cc]mc