Re: About referential integrity.

On Mon, 2002-02-25 at 15:01, BOURIAUD wrote:
> Since I fear I'm not clear in the above, let me show you an example.
> 
> 
> Let's say I create two tables as shown below :
> 
> create table t1
> (
>     key1 serial PRIMARY KEY,
>     field1 varchar(30)
> );
> 
> create table t2
> (
>     key2 serial not null PRIMARY KEY,
>     key1 int4 references t1,
>     field2 varchar(30)
> ); 
> 
> As far as I know, t2 and t1 are linked together. If I want to select rows 
> that belong to both tables, I would have to write something like this :
> select * from t1, t2 where t1.key1 = t2.key1;
> 
> I think this is quite redundant, since I've created my tables so as to make 
> sure that they would respect what is in the select above !!!!
> 
> 
> So, why souldn't I be abble to write :
> select * from t1, t2;
> 
> and have the backend returns me only the rows that have t1.key1 = t2.key2 ???

That is not what SQL does.

The purpose of referential integerity is to ensure that a value in one
table corresponds to a row in another.  It operates on database changes;
it does not extend to select queries.
-- 
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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