Обсуждение: multi-table unique index

-- Suppose I have several types of foos

create table foo_types (   foo_type_id serial primary key,   foo_name text not null
);

-- And the foos itself:

create table foo (   foo_id serial primary key,   foo_type_id int not null references foo_types,   foo_general_data1
text
);

-- 1st special foo:

create table foo_1 (   foo_1_id serial primary key,   foo_id int not null references foo,   foo_1_data1 int,
foo_1_data2text
 
);

-- 2nd special foo:

create table foo_2 (   foo_2_id serial primary key,   foo_id int not null references foo,   foo_2_data1 numeric(8,2),
foo_2_data2timestamp
 
);

-- And I have bars that each have zero or more (special) foos.

create table bar (   bar_id serial primary key
);

create table bar_foos (   bar_id int not null references bar,   foo_id int not null references foo
);

-- Now how do I prevent that I can insert a foo_1 and a foo_2 with
-- the same foo_id? Or is the design errorneous itself?

--
Markus Bertheau
Berlin, Berlin, Germany

Instead of using the "serial" datatype, you can set it to "int4 PRIMARY KEY 
DEFAULT nextval(foo_type_id_seq)" and you can manually create the sequence 
"foo_type_id_seq".

This way all the tables share the same sequence.

On Monday 23 June 2003 06:58 am, Markus Bertheau wrote:
> -- Suppose I have several types of foos
>
> create table foo_types (
>     foo_type_id serial primary key,
>     foo_name text not null
> );
>
> -- And the foos itself:
>
> create table foo (
>     foo_id serial primary key,
>     foo_type_id int not null references foo_types,
>     foo_general_data1 text
> );
>
> -- 1st special foo:
>
> create table foo_1 (
>     foo_1_id serial primary key,
>     foo_id int not null references foo,
>     foo_1_data1 int,
>     foo_1_data2 text
> );
>
> -- 2nd special foo:
>
> create table foo_2 (
>     foo_2_id serial primary key,
>     foo_id int not null references foo,
>     foo_2_data1 numeric(8,2),
>     foo_2_data2 timestamp
> );
>
> -- And I have bars that each have zero or more (special) foos.
>
> create table bar (
>     bar_id serial primary key
> );
>
> create table bar_foos (
>     bar_id int not null references bar,
>     foo_id int not null references foo
> );
>
> -- Now how do I prevent that I can insert a foo_1 and a foo_2 with
> -- the same foo_id? Or is the design errorneous itself?
>
> --
> Markus Bertheau
> Berlin, Berlin, Germany
>
> ---------------------------(end of broadcast)---------------------------
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-- 
Michael A Nachbaur <mike@nachbaur.com>

В Пнд, 23.06.2003, в 19:32, Michael A Nachbaur пишет:
> Instead of using the "serial" datatype, you can set it to "int4 PRIMARY KEY
> DEFAULT nextval(foo_type_id_seq)" and you can manually create the sequence
> "foo_type_id_seq".
>
> This way all the tables share the same sequence.

Yeah, but I want to force this behaviour. so that it cannot happen by
accident when you insert records without relying on the sequence.

--
Markus Bertheau.
Berlin, Berlin.
Germany.

On Monday 23 June 2003 11:16 am, Markus Bertheau wrote:
> В Пнд, 23.06.2003, в 19:32, Michael A Nachbaur пишет:
> > Instead of using the "serial" datatype, you can set it to "int4 PRIMARY
> > KEY DEFAULT nextval(foo_type_id_seq)" and you can manually create the
> > sequence "foo_type_id_seq".
> >
> > This way all the tables share the same sequence.
>
> Yeah, but I want to force this behaviour. so that it cannot happen by
> accident when you insert records without relying on the sequence.

I believe that's what I recommended.  IIRC the "serial" datatype is simply a
shortcut to what I listed above.  This way, if you do not explicitly specify
an id for your record, it'll pull the default; which retrieves a new values
from the sequence.

If you want to ensure that a value is unique when a record is inserted, even
if the user explicitly specifies an ID values, you can create a unique
trigger on the tables, but this depends on what you want to do.

В Пнд, 23.06.2003, в 20:34, Michael A Nachbaur пишет:
> On Monday 23 June 2003 11:16 am, Markus Bertheau wrote:
> > В Пнд, 23.06.2003, в 19:32, Michael A Nachbaur пишет:
> > > Instead of using the "serial" datatype, you can set it to "int4 PRIMARY
> > > KEY DEFAULT nextval(foo_type_id_seq)" and you can manually create the
> > > sequence "foo_type_id_seq".
> > >
> > > This way all the tables share the same sequence.
> >
> > Yeah, but I want to force this behaviour. so that it cannot happen by
> > accident when you insert records without relying on the sequence.

> If you want to ensure that a value is unique when a record is inserted, even
> if the user explicitly specifies an ID values, you can create a unique
> trigger on the tables, but this depends on what you want to do.

I believe what you described is what I want to do. What's a unique
trigger, though?

--
Markus Bertheau.
Berlin, Berlin.
Germany.

On Monday 23 Jun 2003 2:58 pm, Markus Bertheau wrote:
> -- Suppose I have several types of foos
>
> create table foo_types (
>     foo_type_id serial primary key,
>     foo_name text not null
> );
>
> -- And the foos itself:
>
> create table foo (
>     foo_id serial primary key,
>     foo_type_id int not null references foo_types,
>     foo_general_data1 text
> );
>
> -- 1st special foo:
>
> create table foo_1 (
>     foo_1_id serial primary key,
>     foo_id int not null references foo,
>     foo_1_data1 int,
>     foo_1_data2 text
> );

An alternative to Markus' ideas in the other thread - store the type in
foo/foo_1, then have a foreign key over both. The irritating thing is that
you're duplicating the type info unnecessarily.

CREATE TABLE foo (foo_id   serial unique,foo_type_id int not null references foo_types,...PRIMARY KEY
(foo_id,foo_type_id)
);

CREATE TABLE foo_1 (extra_foo   int4 not null,extra_type int4 not nullextra1    text,PRIMARY KEY (extra_foo,
extra_type)CONSTRAINTlink_to_foo FOREIGN KEY (extra_foo,extra_type) REFERENCES foo_core  
(foo_id, foo_type_id)
);


--  Richard Huxton