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Re: Aggregate and join problem

From: "Oliveiros d'Azevedo Cristina" <oliveiros(dot)cristina(at)marktest(dot)pt>
To: Swärd Mårten <Marten(dot)Sward(at)sweco(dot)se>,<pgsql-sql(at)postgresql(dot)org>
Subject: Re: Aggregate and join problem
Date: 2012-03-01 11:04:28
Message-ID: 6642CFF102224D2492403CEC553EB3E3@marktestcr.marktest.pt (view raw or flat)
Thread:
Lists: pgsql-sql
Great to Hear!

Best,
Oliver
  ----- Original Message ----- 
  From: Swärd Mårten 
  To: Oliveiros d'Azevedo Cristina ; pgsql-sql(at)postgresql(dot)org 
  Sent: Thursday, March 01, 2012 11:01 AM
  Subject: Re: [SQL] Aggregate and join problem


  It worked like a charm! Many thanks for that great solution!

  Best regards, Mårten



  Från: Oliveiros d'Azevedo Cristina [mailto:oliveiros(dot)cristina(at)marktest(dot)pt] 
  Skickat: den 1 mars 2012 11:49
  Till: Swärd Mårten; pgsql-sql(at)postgresql(dot)org
  Ämne: Re: [SQL] Aggregate and join problem



  Hi, Swärd,



  As you didn't name your tables' columns I decided to call them col1, col2, etc.



  I dunno if this will do what you want as it is completely untested code.



  But, give it a try and see if it works and if it doesn't, tell me the error, and we'll continue from there.

  You'll have to substitute my col1, col2, etc with your actual column names.



  Best,

  Oliveiros





  SELECT query1.t1_id, t1.col2,t1.col3,t1.col4, query1.minimum

  FROM (

  SELECT t3.col2 as t1_id, MIN(t2.col2) as minimum

  FROM Table_3 t3 

  JOIN Table_2 t2

  ON t3.col1 = t2.col1

  GROUP BY t3.col2

  ) query1

  JOIN  Table_1 t1

  ON t1.col1 = query1.t1_id



    ----- Original Message ----- 

    From: Swärd Mårten 

    To: pgsql-sql(at)postgresql(dot)org 

    Sent: Thursday, March 01, 2012 10:30 AM

    Subject: [SQL] Aggregate and join problem



    Hi folks

    I have some troubles to create a SQL-query and my hope is that someone of you could help me with this..

    It's somewhat difficult to explain what I want to do but I'll give it a try and see if you can understand the problem.. Ahh fuck this.. It's almost imposible to explain.. J I don't understand what it mys self after I have written it.. Read and see if you understand.. J 



    I have three tables:



    Table_1:

    A table with meta data for areas (names, geometries and so..). Every area has a unique id.

    Example:

    101 | 'small area' | 'area name' | geom 

    102 | 'small area' | 'area name' | geom.

    103 | 'small area' | 'area name' | geom.

    104 | 'LARGE area' | 'area name' | geom



    Table 2.

    A table with values for some smaller areas. Contains a reference to an id in table1 and a value

    Example:

    101 | 12.5

    102 | 5.5

    103 | 6.5





    Table_3:

    A cross reference table with id:s for witch areas are connected to each other. Eg. What smaller areas that's is inside a larger area.

    A larger area could have many smaller areas connected to it

    Contains a reference to table 1 for the smaller areas and a reference to table 1 for the larger area. 

    Example:

    101 | 104

    102 | 104

    103 | 104





    What I want to do is the following:

    The larger area should "inherit" the lowest value from the smaller areas that are connected to it.



    I want to be able to get all larger areas and let them have a value that is the lowest value from table 2.

    If you look at the example data I only want to get the larger area (104) from table 1 with a value from table 2 that is the lowest value of the  areas connected to id 104. The result would be: 104 | 'LARGE area' | 'area name' | geom. | (value from table 2 id 102)



    Best regards, Mårten

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