[cc]mc |
.hd rddiff "take the difference of two relations" 07/01/82
rddiff
.ds
'Rddiff' is part of the toy relational data base system, 'rdb'.  It
creates a new relation by performing the set difference 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 new relation is formed by examining both input relations and
retaining those rows that are in the first relation (standard input 1)
but not in the second relation (standard input 2).  The remaining rows
of both relations are discarded.
.nf

     For example:

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

       p1.rel> p2.rel> rddiff >p.rel

                     p.rel --------------
                           |code | name |
                           --------------
                           | 101 | ink  |
                           --------------

.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> rddiff >p.rel
p.des> newp.data> rdmake | p.rel> rddiff >newp.rel
.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),
rddiv (1),
rdint (1),
rdmax (1),
rdmin (1),
rdnat (1),
rdsum (1)
[cc]mc
