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Re: A question about inheritance

From: Oliver Elphick <olly(at)lfix(dot)co(dot)uk>
To: li li <lili(at)cs(dot)uoregon(dot)edu>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: A question about inheritance
Date: 2002-12-31 01:42:49
Message-ID: 1041298969.22899.27.camel@linda.lfix.co.uk (view raw or flat)
Thread:
Lists: pgsql-performance
On Sun, 2002-12-29 at 22:09, li li wrote:
> Hi,
>    As we can see all tuples of a child table when scanning parent table,
> I'm confused about if that means there are two copies that are stored on
> disk, one is for child table, and the other for parent table? If so,
> I have to reconsider the size of my database.

When you select from the parent table, all rows in its children are also
selected unless you use the keyword ONLY.

So 

  SELECT * FROM parent;

will show all rows of parent and children. But

  SELECT * FROM ONLY parent;

will show just the rows in the parent table.

-- 
Oliver Elphick                                Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight, UK                             http://www.lfix.co.uk/oliver
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839  932A 614D 4C34 3E1D 0C1C
                 ========================================
     "Ye have heard that it hath been said, Thou shalt love 
      thy neighbour, and hate thine enemy. But I say unto 
      you, Love your enemies, bless them that curse you, do 
      good to them that hate you, and pray for them which 
      despitefully use you, and persecute you;"          
                                     Matthew 5:43,44 


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