Date: Sun, 15 Oct 2006 11:23:01 -0400
From: Daniel CAUNE <d.caune@free.fr>
Subject: Re: migrating numeric to serial from MSSQL to postgres
In-reply-to: <45323DA5.1080601@ashtonwoodshomes.com>
To: 'Terry Fielder' <terry@ashtonwoodshomes.com>,
	'Kenneth Gonsalves' <lawgon@thenilgiris.com>
Cc: pgsql-sql@postgresql.org
Message-id: <001001c6f06d$cdd508b0$0b00a8c0@tedy>
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> I believe:
> IDENTITY(1, 1) just means "Primary Key" in M$SQL
> 

IDENTITY is not obligatory a primary key.  It's an auto-incremented column.
It might correspond to a PostgreSQL sequence.

[http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts
_ia-iz_3iex.asp]

> numeric 18,0 means a numeric field of zero decimal points.  Hence we are
> looking at a 18 byte integer.  bigint is not big enough, so probably
> should use the same in numeric 18,0 in postgres
> 

numeric[ (precision[ , scale] )], where precision refers to the maximum
total number of decimal digits that can be stored.  The default precision is
18, and for such a value the storage is of 9 bytes.

[http://msdn2.microsoft.com/en-us/library/ms187746.aspx]

Because it seems that a default value has been used here, I'd say that
Kenneth doesn't have any particular requirement, haven't you Kenneth?... :-)
An int or a bigint would be perhaps sufficient.  My two cents.


I don't know whether Kenneth requires migrating database structure only or
whether he needs to migrate data too.

When migrating data, Kenneth might want to define a sequence which start
value begins at the next value of its IDENTITY column (cf.
IDENT_SEED(my_table)).

[http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts
_ia-iz_9yxw.asp]

Kenneth might want to transfer his data first and to define the sequence
after (for transfer performance reason?):

CREATE TABLE my_table
(
  Id INTEGER NOT NULL,
  ...
);

[DTS process here]

CREATE SEQUENCE my_sequence
  INCREMENT BY 1
  MINVALUE 1
  NO MAXVALUE
  START WITH <IDENTITY current value + 1>
  CACHE 1
  NO CYCLE;

ALTER TABLE m_table
  ALTER COLUMN Id SET DEFAULT NEXTVAL('my_sequence');

Does that make sense?


--
Daniel