On Jul 12, 2006, at 7:38 PM, Adrian Holovaty wrote:
>
> On 7/12/06, Jay Parlar <[EMAIL PROTECTED]> wrote:
>> Is there a better way to do this? More specifically, an atomic way to
>> generate and set the new unique_id? I can't just use the
>> autogenerated
>> 'id' primary key as an unique identifier, because I have a list of
>> legacy unique_id values which I have to initially populate the db
>> with.
>
> Use the auto-incrementing "id" field. Populating the DB with some
> explicit values shouldn't pose any problems in that case.
The only caveat is that the auto increment is not smart enough to
skip over values that already exist (in Postgres anyway, sequences
are simple number generators that know nothing about the table they
generate values for). So you need to set the starting sequence value
greater than the maximum value in the table, otherwise you'll get
unique key constraint violations on insertions. If you're pre-
populating the table with data in your sql initialization, at the
end, make sure to prime the sequence using the setval function, like
this:
SELECT setval('mytable_seq_id', 999);
In this case, 999 is the current maximum value, 1000 will be the next
returned sequence id.
Don
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