Re: How to fill empty column with number sequence?
Date: Wed, 18 Feb 2004 18:07:38 -0500
Message-ID: <e6udnR_XcZodba7dRVn-vA_at_comcast.com>
"steve" <me_at_me.com> wrote in message
news:0001HW.BC5A003200008C96F03055B0_at_news.newsguy.com...
| On Fri, 13 Feb 2004 16:11:25 +0800, Ken1 wrote
| (in article <3bb6578e.0402130011.75bd6b51_at_posting.google.com>):
|
| > I am going to drop a primary key from one column and create a new
| > column to be used as primary key in an existing database.
| > The old column was a date column which someone earlier though was a
| > good candidate for a primary key which we all know it's not.
| >
| > Now I want to add a new field, i.e. called ID, with a normal number
| > sequence as primary key.
| >
| > I have dropped the primary key, created the new column, created the
| > new sequence and created a trigger to generate the primary key for new
| > inserts.
| >
| > But I don't know how to generate/update the new ID column with
| > sequence numbers for the already existing records.
| >
| > Any ideas?
| >
| > /Kenneth
|
| create a sequence.
| when you add the new col to the table ,
| in the default value for the col , query the sequence.
|
| this will add a new col with the values already installed.
|
| then for future additions add a trigger. that calls the sequence whenever
the
| table is inserted.
|
| or you could be real lazy an just leave the default value in place.
|
|
|
you can't use a sequence as a default value
from the SQL manual:
DEFAULT specifies a value to be assigned to the column if a subsequent INSERT statement omits a
value for the column. The datatype of the expression must match the datatype of the
column. The column must also be long enough to hold this expression. For the syntax of
expr, see "Expressions" on page 5-1.
Restriction: A DEFAULT expression cannot contain references to other columns, the
pseudocolumns CURRVAL, NEXTVAL, LEVEL, and ROWNUM, or date constants that are not
fully specified.
note also that the default value can be overridden, including with an explicit null (making default values basically useless)
but you can use the sequence in an update clause
update x
set id = x_seq.nextval;
- mcs