Re: master-detail relationship and count

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
>
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>
>
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==================================================================
Achilleus Mantzios
S/W Engineer
IT dept
Dynacom Tankers Mngmt
Nikis 4, Glyfada
Athens 16610
Greece
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email:  achill@matrix.gatewaynet.com       mantzios@softlab.ece.ntua.gr