> Hi,
>
> Can someone show me example when it is usefull to

have different field

> type in relation
>
> Sample
>

Create table test1 (id smallint not null primary key)

>
> Create

table test2 (id1 integer)

>
> Alter table test2 Add foreign key

(id1) references test1(id)

>
> Why this is not

forbidden?

Perhaps cause the referenced column in table test1 can only store a
subset (SMALLINT) of the value range of the INTEGER used in test2?

Even if this works at DDL time, I wonder how strict the optimizer then
is in JOIN statements using an index. Haven't tried.

At DDL time: What happens if you flip the used data types for ID/ID1?

--
With regards,
Thomas Steinmaurer
http://www.upscene.com/

Professional Tools and Services for Firebird
FB TraceManager, IB LogManager, Database Health Check, Tuning etc.