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. >
>Supposerelations 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
valueof >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
shouldreturn: > > s >---- > s1
 
SELECT DOR.s FROM DEND,DOR WHERE DOR.p = DEND.p;

-- 
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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