[cc]mc |
.hd rddiv "perform the division of two relations" 07/01/82
rddiv
.ds
'Rddiv' is part of the toy relational data base system, 'rdb'.  It
creates a new relation by performing the set division of the two
relations specified as standard inputs 1 and 2 and writes the
resulting new relation on standard output.
.sp
Standard input 1 is the dividend, standard input 2 is the divisor, and
standard output (the resulting relation) is the quotient. The quotient
consists of those rows of the dividend, projected onto the attributes
not in the division, whose corresponding
attributes include every row of the divisor.  In other words, a
row X will appear in the quotient if and only if the pair <X,Y>
appears in the dividend for all rows Y appearing in the divisor.
.nf

     For example:

       p1.rel  --------------      p2.rel --------
               |code | name |             | name |
               --------------             --------
               | 100 | pens |             | pens |
               |-----|------|             |------|
               | 100 | ink  |             | ink  |
               |-----|------|             --------
               | 100 | ruler|
               |-----|------|
               | 101 | pens |
               |-----|------|
               | 101 | paper|
               |-----|------|
               | 102 | ink  |
               |-----|------|
               | 103 | ink  |
               |-----|------|
               | 103 | pens |
               --------------


       p1.rel> p2.rel> rddiv >p.rel

                     p.rel -------
                           | code |
                           --------
                           | 100  |
                           |------|
                           | 103  |
                           --------

.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 the terminal; otherwise,
the output relation is
written in binary internal format for processing by other 'rdb'
programs.
.sp
Identical tuples are not removed from the resulting relation.  These
can be removed using 'rdsort' and 'rduniq'.
.es
p1.rel> p2.rel> rddiv >p.rel
p1.rel> p2.rel> rddiv | rdsort | rduniq | rdprint
.me
"Sorry, a relation can't be read from the terminal"
.br
"relation is corrupted!!"
.br
"Cannot load input relation 1"
.br
"Cannot load input relation 2"
.br
"Relation 2 has domain not defined in relation 1"
.br
"Couldn't rewind sort file 1"
.br
"Couldn't rewind sort file 2"
.br
"Error on sort file 2"
.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),
rdint (1),
rdmax (1),
rdmin (1),
rdnat (1),
rdsum (1)
[cc]mc