Message-ID: <43F9A1BA.4020305@anpe.fr>
Date: Mon, 20 Feb 2006 12:02:18 +0100
From: Patrick JACQUOT <patrick.jacquot@anpe.fr>
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To: pgsql-sql@postgresql.org
Subject: Re: SELECT on a to-be-determined table
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garhone wrote:

>Hi,
>
>I'm a new at this. So please forgive if I mess up. Also, if there is
>already a reference/tutorial somewhere, feel free to point me to it.
>
>Here's my situation:
>db=# select * from projects;
> projid | projname
>--------+----------
>      1 | cars
>      2 | houses
>      3 | pets
>(3 rows)
>
>db=# select * from cars;
> carid | carname
>-------+---------
>     1 | ford
>     2 | mazda
>(2 rows)
>
>db=# select * from houses;
> houseid | housename
>---------+-----------
>       1 | semi
>       2 | trailer
>       3 | mansion
>(3 rows)
>
>db=# select * from pets;
> petid | petname
>-------+---------
>     1 | dog
>     2 | cat
>     3 | bird
>(3 rows)
>
>Is it possible to do this:
>Give me all the rows of the table whose project id is 2 (or whatever
>projid).
>
>Thanks
>
>
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>
Your way of thinking leads to the need of comparing a field to a table name.
Such a request requires two steps
1 - retrieve the name of the table to search in, store it in a variable
2 - use execute to issue a request to that table.

Instead, I think it would be better to use only two tables:
1 - projects (projid, projname)
2 - items (itemid, projid, itemproperty1,itemidproperty2,...)
You would have in the second table, to take your example:
projid | itemid | itemname               |
     1 |      1 | ford                   |
     1 |      2 | mazda                  |
     2 |      1 | semi                   |
     2 |      2 | trailer                |
     2 |      3 | mansion                |
     3 |      1 | dog                    |
     3 |      2 | cat                    |
     3 |      3 | bird                   |
Your request would become :
SELECT itemid, itemname FROM items where projid=2

The problem of having a different set of properties
for the items of differents projects could be solved with three tables:
project(projid, projname)
itempropertymeaning(projid, propid, propmeaning)
itemproperty(projid, itemid, propid, propvalue)