[thelist] Shell Script Basics?
rudy
r937 at interlog.com
Wed May 23 15:09:25 CDT 2001
>(Well, almost. They ain't got no books on wimmen....)
yeah, that one ain't been written yet
i can contribute several chapters, though, except they won't do anybody any
good except me, and for me any advice along those lines is already too
little too late...
<tip>
a many-to-many database relationship is best visualized as two intersecting
heirarchies
skill -- person is 1-m
a skill may be possessed by several persons
person -- skill is 1-m
a person may possess several skills
the intersection is implemented in a "relationship" or "intersection" table
(a "junction" table in the old codasyl network database terminology)
the intersection table, personskill, is a child of both the skill table and
the person table simultaneously
add some skills
01 html
02 javascript
03 css
04 cf
05 sql
add some persons
934 joe
935 fred
936 mary
937 rudy
add some personskills
934 01
934 03
936 04
937 04
937 05
list the skills of a particular person
select skillname
from person join personskill join skill
where personid=937
returns
cf
sql
list the persons who have a particular skill
select personname
from skill join personskill join person
where skillid=03
returns
joe
finding people who have a particular *set* of skills (e.g. 03 *and* 04) is
a little trickier but still straightforward (it involves subselects)
</tip>
rudy
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