[cc]mc |
.hd rdavg "compute the average value of an attribute" 07/01/82
rdavg [<selection expr>] <attr>
.ds
'Rdavg' is part of the toy relational data base management system, 'rdb'.
It computes the average value of a specified attribute over all rows of
the relation that satisfy the optional select expression.  If no select
expression is given then it computes the average of an attribute over all
rows of the relation.  Standard input 1 must be directed to a file
containing an 'rdb' relation.  The result is written to standard output.
.sp
The input relation must be a file containing a relation that was created
by 'rdmake' or other 'rdb' programs; the relation cannot be read from the
terminal.  The select expression is formed from the logical operators
"&" (and), "|" (or), and "~" (not) connecting relational conditions
involving two domains or a domain and a literal.
.es
p.rel> rdavg weight
p.rel> rdavg "height>65&height<80" weight
.me
"Sorry, a relation can't be read from the terminal"
.br
"relation is corrupted!!"
.br
"Cannot load input relation"
.br
"Usage: rdavg [<selection expr>] <attr>"
.br
"Domain not found"
.br
"Strings can't be averaged"
.br
"Average is undefined for empty relation"
.br
"Invalid expression"
.br
"expected domain name or literal"
.sa
rdcat (1),
rdextr (1),
rdjoin (1),
rdmake (1),
rdprint (1),
rdproj (1),
rdsel (1),
rdsort (1),
rduniq (1),
rdatt (1),
rdcount (1),
rddiff (1),
rddiv (1),
rdint (1),
rdmax (1),
rdmin (1),
rdnat (1),
rdsum (1)
[cc]mc