Обсуждение: Sequence

Hello.
A table has two primary keys: CREATE TABLE example ( pk1 integer, pk2
integer, PRIMARY KEY (pk1, pk2) ). To add a new record I use command:
INSERT INTO example (pk1, pk2) VALUES (0, 0). Before adding the new
record I have to find out the last value of pk2. How can I use something
like this: INSERT INTO example (pk1, pk2) VALUES (0, nextval('pk2'))?
If a table just has one primary key I can use sequence (CREATE
SEQUENCE). What about two primary keys?

am  Fri, dem 25.07.2008, um 15:54:23 +1100 mailte Alex Cheshev folgendes:
> Hello.
> A table has two primary keys: CREATE TABLE example ( pk1 integer, pk2
> integer, PRIMARY KEY (pk1, pk2) ). To add a new record I use command:
> INSERT INTO example (pk1, pk2) VALUES (0, 0). Before adding the new
> record I have to find out the last value of pk2. How can I use something
> like this: INSERT INTO example (pk1, pk2) VALUES (0, nextval('pk2'))?
> If a table just has one primary key I can use sequence (CREATE
> SEQUENCE). What about two primary keys?

You can also use a sequence.

Regards, Andreas
--
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID:   0x3FFF606C, privat 0x7F4584DA   http://wwwkeys.de.pgp.net

Alex Cheshev wrote:
> Hello.
> A table has two primary keys:

It appears that you really meant "a table has a two-field composite
primary key". There can only be one primary key for a table, that's the
whole point - but the primary key can be composed of more than one field.

[Note: if you format your SQL when you post, more people will bother to
read it and try to help you out. For example, your CREATE TABLE could've
been better written as:]

> CREATE TABLE example (
 >   pk1 integer,
 >   pk2 integer,
>   PRIMARY KEY (pk1, pk2)
> );

> To add a new record I use command:

> INSERT INTO example (pk1, pk2) VALUES (0, 0).

> Before adding the new
> record I have to find out the last value of pk2. How can I use something
> like this:

> INSERT INTO example (pk1, pk2) VALUES (0, nextval('pk2'))

> ?

> If a table just has one primary key I can use sequence (CREATE
> SEQUENCE). What about two primary keys?

You can still use a SERIAL type or manually use CREATE SEQUENCE and
nextval() .

I suspect I'm missing the point of your question, though. Perhaps if you
gave a real-world example of what you are trying to do, with meaningful
field names?

--
Craig Ringer