Re: Joining a result set from four (4) tables - Mailing list pgsql-sql

Hi Aaron,

Thanks very much, I really appreciate both the solution and the advice 
about naming conventions. Your script worked fine and gives me an 
example of what to do for other situations as well.

Because the logic structure of this software is in the front end 
application rather than the database there is a strong need to keep the 
naming of fields generic rather than specific, I am not using 
pre-defined foreign keys at all. If I was building the database with a 
purpose specific goal I would be doing what you say. I have found though 
that when I label elements at different levels of the back end for one 
purpose, they are less transportable in the long run. In this case the 
naming conventions are actually stored in another table and applied as 
aliases when needed. That way I can change the names and labels (for a 
new client or industry) while the underlying structure remains the same. 
I hope to increase interoperability in this way as well.

Thanks again for your help.

Kind regards

John T.



Aaron Bono wrote:
>
> First of all, I must say it is very unfortunate that all the tables 
> have the same name for their primary key column.  It made things 
> confusing at first when reading through the tables (the foreign key 
> names don't match the primary keys they map to).  It also makes it 
> more likely you will do a join improperly.
>
> Worse, your foriegn key names are very ambiguous.  The name related_id 
> says nothing about what table it maps to.  That means you need 
> documentation or the foreign key definitions (are you using foreign 
> key constraints?) to tell what is going on.
>
> Anyway... on to solving your problem.
>
> SELECT
>   permission.serial_id,
>   resource.name <http://resource.name/>,
>   actions.name <http://actions.name/>,
>   actions.classification,
>   actions.display_group
> FROM permission
> INNER JOIN policies ON (
>   policies.serial_id = permission.related_id
> )
> INNER JOIN actions ON (
>   actions.serial_id = policies.related_id
> )
> INNER JOIN resource ON (
>   -- This is tricky as policies maps to resources AND actions maps to 
> resources
>   -- so the real question is which one do you do?  I did both.
>   policies.resource_id = resources.serial_id
>   AND
>   actions.related_id = resources.serial_id
> )
> WHERE
>   permission.user_id = '11' AND
>   policies.status = 'Active' AND
>   permission.status = 'Active'AND
>   actions.status = 'Active'AND
>   resource.status = 'Active'
> ;
>
> I always discourage listing more than one table in the FROM clause.  
> Use INNER and OUTER JOINs - it is much easier to debug and it is 
> somewhat self documenting.  That way, when you or another developer 
> look at this in the future, you understand right away how the tables 
> are being put together.
>
> ==================================================================
>    Aaron Bono
>    Aranya Software Technologies, Inc.
>    http://www.aranya.com
> ==================================================================