Re: master-detail relationship and count

On Fri, 29 Nov 2002, Gary Stainburn wrote:

> As you can see from the extract below, your statement has worked for all
> landmarks that have links, but ignores any landmarks with out links. How can
> I adjust this so that all landmarks are listed, but with a zero count where
> appropriate?

Then, use LEFT OUTER JOIN ... USING (),
in combination with COALESCE().

(read the docs)

>
> select r.rtid, r.rtname, subsel.cnt from route r,
> (select r2.rtid as rid, count(lnk.lkid) as cnt from route r2,links lnk
> where lnk.lktype='R'
> and lnk.lklid = r2.rtid group by r2.rtid) as subsel
> where r.rtid = subsel.rid;
> [gary(at)larry gary]$ psql -d nymr <route.sql
> rtid | rtname | cnt
> ------+------------+-----
> 1 | The Grange | 1
> (1 row)
> [gary(at)larry gary]$
>
> Gary
>
> On Friday 29 Nov 2002 10:36 am, Achilleus Mantzios wrote:
> > On Fri, 29 Nov 2002, Gary Stainburn wrote:
> > > Hi folks.
> > >
> > > I've got a master detail relationship where I have a railway route table
> > > listing landmarks along the route, and a Links table listing URL's
> > > associated with that landmark. Listed below:
> > >
> > > How can I do a query showing the landmark ID, the landmark name, and a
> > > count of links associated with that landmark. Below is a SQL statement
> > > that although is illegal, gives a good idea of what I'm looking for.
> > >
> > > select r.rtid, r.rtname, l.count(*) from route r, links l where l.lktype
> > > = 'R' and l.lklid = r.rtid;
> >
> > select r.rtid,r.rtname,subsel.cnt from route r,
> > (select r2.rtid as rid,count(lnk.lkid) as cnt from route r2,links lnk
> > where lnk.type='R'
> > and lnk.lklid = r2.rtid group by r2.rtid) as subsel
> > where r.rtid = subsel.rid
> >
> > or something like that.
> >
> > > nymr=# \d route
> > > Table "route"
> > > Attribute | Type | Modifier
> > > ------------+-----------------------+------------------------------------
> > >-------------- rtid | integer | not null default
> > > nextval('route_rtid_seq'::text)
> > > rtmile | integer | not null
> > > rtyards | integer | not null
> > > rtname | character varying(40) |
> > > rtspeed | integer |
> > > rtgradient | integer |
> > > rtsection | integer |
> > > rtphone | character(1) |
> > > rtcomments | text |
> > > Indices: route_index,
> > > route_rtid_key
> > >
> > > nymr=# select r.rtid, l.count(*) from route r, links l where
> > > nymr=# \d links
> > > Table "links"
> > > Attribute | Type | Modifier
> > > -----------+-----------------------+-------------------------------------
> > >------------ lkid | integer | not null default
> > > nextval('staff_sid_seq'::text)
> > > lkdesc | character varying(40) |
> > > lkurl | character varying(40) |
> > > lktype | character(1) |
> > > lklid | integer |
> > > Index: links_lkid_key
> > >
> > > lktype indicates the link type - 'R' indicates a route entry
> > > lklid indicates the link ID. For a 'R' it is the rtid of the route entry
> > > --
> > > Gary Stainburn
> > >
> > > This email does not contain private or confidential material as it
> > > may be snooped on by interested government parties for unknown
> > > and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
> > >
> > >
> > > ---------------------------(end of broadcast)---------------------------
> > > TIP 4: Don't 'kill -9' the postmaster
> >
> > ==================================================================
> > Achilleus Mantzios
> > S/W Engineer
> > IT dept
> > Dynacom Tankers Mngmt
> > Nikis 4, Glyfada
> > Athens 16610
> > Greece
> > tel: +30-10-8981112
> > fax: +30-10-8981877
> > email: achill(at)matrix(dot)gatewaynet(dot)com
> > mantzios(at)softlab(dot)ece(dot)ntua(dot)gr
>
> --
> Gary Stainburn
>
> This email does not contain private or confidential material as it
> may be snooped on by interested government parties for unknown
> and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
>
>

==================================================================
Achilleus Mantzios
S/W Engineer
IT dept
Dynacom Tankers Mngmt
Nikis 4, Glyfada
Athens 16610
Greece
tel: +30-10-8981112
fax: +30-10-8981877
email: achill(at)matrix(dot)gatewaynet(dot)com
mantzios(at)softlab(dot)ece(dot)ntua(dot)gr