Обсуждение: Adding a default value to a column after it exists
Is there a way to add a default value definition to an existing column? Something like an "alter table... alter column... default 'foo'".
I thought of a clumsy way to do this... create a temp column, set it's value to that of the column to be altered, drop the column to be altered, redefine it with the default, shunt all the values in the temp column over to the new column and then drop the temp column. But I have before and after triggers on the table that react to changes in this column (not to mention the need for it's existence).
I could add something to the before trigger to do this too. But it would be cleaner to do this as a column property.
Thanks for any help.
Hi Dave, On 13/04/11 17:21, Gauthier, Dave wrote: > > Is there a way to add a default value definition to an existing > column? Something like an "alter table... alter column... default 'foo'". > Sure is something like that: ALTER TABLE tablename ALTER COLUMN columnname SET DEFAULT expression; For full documentation see: http://www.postgresql.org/docs/9.0/static/sql-altertable.html > Thanks for any help. > Regards, -- Mike Fowler Registered Linux user: 379787
"Gauthier, Dave" <dave.gauthier@intel.com> writes:
> Is there a way to add a default value definition to an existing column? Something like an "alter table... alter
column...default 'foo'".
ALTER TABLE ... ALTER COLUMN ... SET DEFAULT ...
regards, tom lane
On Wed, Apr 13, 2011 at 09:21:20AM -0700, Gauthier, Dave wrote: > Is there a way to add a default value definition to an existing column? Something like an "alter table... alter column...default 'foo'". ALTER TABLE table ALTER [ COLUMN ] column SET DEFAULT expression (see http://www.postgresql.org/docs/9.0/interactive/sql-altertable.html) Note that this doesn't actually update the fields that are NULL in the column already. For that, once you had the default in place, you could do UPDATE table SET column = DEFAULT WHERE column IS NULL IIRC. A -- Andrew Sullivan ajs@crankycanuck.ca
In article <20110413163120.GU24471@shinkuro.com>, Andrew Sullivan <ajs@crankycanuck.ca> writes: > On Wed, Apr 13, 2011 at 09:21:20AM -0700, Gauthier, Dave wrote: >> Is there a way to add a default value definition to an existing column? Something like an "alter table... alter column...default 'foo'". > ALTER TABLE table ALTER [ COLUMN ] column SET DEFAULT expression > (see http://www.postgresql.org/docs/9.0/interactive/sql-altertable.html) > Note that this doesn't actually update the fields that are NULL in the > column already. For that, once you had the default in place, you > could do > UPDATE table SET column = DEFAULT WHERE column IS NULL And you probably want to do ALTER TABLE table ALTER [ COLUMN ] column SET NOT NULL after that.