Hi Matteo,

First, I send allready a correction but it apears it didn't got there ! It
was:

========= Correction message =========
Correction !

> create table FILES (
> id integer not null,
> file varchar(200) not null,
> constraint FILES_PK primary key (id, file)
> );

The above one is wrong ! Replace it with this !

create table FILES (
id integer not null,
name varchar(200) not null,
constraint FILES_PK primary key (id),
constraint FILES_NAME_UK unique (name)
);

So, for each (unique) id you'll have an unique file name.

========= End correction message =========


Second,

From: "Matteo Giacomazzi" <matteo.giacomazzi@...>

> HB> If you want a column or group to be a key, you must apply the
> HB> appropriate constraint. And don't create additional indexes that
> HB> are identical to the constraint indexes!!
>
> Okay: now I'm confused! :)
> What's the difference between an UNIQUE CONSTRAINT and an UNIQUE KEY
> CONSTRAINT?
> Is it only a logical one?
> I mean: a foreign key may references a primary key and an unique key
> but it cannot reference an unique constraint wich is not key?

No, It's a matter of classification:
- a UNIQUE KEY is a CONSTRAINT
- a FOREIGN KEY is a CONSTRAINT
- a CHECK is, also, a CONSTRAINT
- a column NOT NULL is a CONSTRAINT

Another thing is that:
- a FOREIGN KEY can reference only a PRIMARY KEY or a UNIQUE KEY.

What Helen wanted to said is that when you make a unique key constraint or a
foreign key constraint IB automatically makes an index on the key fields
(you can see it with an admin tool, it has a system generated name).

That's all.

Regards !
Raul.



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