Re: Need help in composing PostgreSQL query

"Vladimir V. Zolotych" wrote:
>Hi
>
>Please help me compose the query in PostgreSQL.
>Using PostgreSQL 7.1.2.
>
>Suppose relations A and B have columns:
> {X1, X2, ..., Xm, Y1, Y2, ..., Yn}
>and
> {Y1, Y2, ..., Yn}
>Attributes Y1, Y2, ..., Yn are common for both relations
>and have the same type in both.
>
>How can I define in PostgreSQL the query producing
>relation with columns X1,X2,...,Xm containing all those tuples
>satisfying conditon: relation A contains tupple
> {x1,x2,...xm,y1,y2,...,yn}
>for _each_ tupple
> {y1,y2,...,yn}
>in relation B ? Where x1 denotes particular value of
>colum X1 etc.

You seem to be talking about a natural join:

SELECT *
FROM a,b
WHERE a.y1 = b.y1 AND a.y2 = b.y2 AND ... AND a.yn = b.yn;

>For example: consider two tables DEND and DOR.
>
>DEND DOR
>
> s | p p
>----+---- ----
> s1 | p1 p1
> s1 | p2 p2
> s1 | p3 p3
> s1 | p4 p4
> s1 | p5 p5
> s1 | p6 p5
> s2 | p1 (6 rows)
> s2 | p2
> s3 | p2
> s4 | p2
> s4 | p4
> s4 | p5
>(12 rows)
>
>For such tables our desired query should return:
>
> s
>----
> s1

SELECT DOR.s
FROM DEND,DOR
WHERE DOR.p = DEND.p;

--
Oliver Elphick Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight http://www.lfix.co.uk/oliver
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