update set x=(subquery on same table)

[CSN]

I'm trying to do:

update nodes n1 set n1.parent_id=(select n2.id from
nodes n2 where n2.key=n1.parent_id);

To set parent_id to the id of the parent (rather than
the key). Would UPDATE FROM fromlist work? I couldn't
find any examples of it's use.

TIA,
CSN

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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match

[Martijn van Oosterhout]

On Fri, Feb 13, 2004 at 12:18:14AM -0800, CSN wrote:

I'm trying to do:

update nodes n1 set n1.parent_id=(select n2.id from
nodes n2 where n2.key=n1.parent_id);

To set parent_id to the id of the parent (rather than
the key). Would UPDATE FROM fromlist work? I couldn't
find any examples of it's use.
See the online help:

# \h update
Command: UPDATE
Description: update rows of a table
Syntax:
UPDATE [ ONLY ] table SET col = expression [, ...]
[ FROM fromlist ]
[ WHERE condition ]

So try:

update nodes set parent_id=n2.id FROM nodes n2 where n2.key=nodes.parent_id;

Unfortunatly you can't alias the table you're updating, but you can alias
the rest.
--
Martijn van Oosterhout <kl*****@svana.org> http://svana.org/kleptog/ (... have gone from d-i being barely usable even by its developers
anywhere, to being about 20% done. Sweet. And the last 80% usually takes
20% of the time, too, right?) -- Anthony Towns, debian-devel-announce

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[CSN]

That does the trick. I'd also like to figure out a way
to set all parent_ids to NULL if no parent row can be
found. I haven't been able to figure it out so far.

Thanks,
CSN
--- Martijn van Oosterhout <kl*****@svana.org> wrote:

On Fri, Feb 13, 2004 at 12:18:14AM -0800, CSN wrote:

I'm trying to do:

update nodes n1 set n1.parent_id=(select n2.id from

nodes n2 where n2.key=n1.parent_id);

To set parent_id to the id of the parent (rather

than

the key). Would UPDATE FROM fromlist work? I

couldn't

find any examples of it's use.

See the online help:

# \h update
Command: UPDATE
Description: update rows of a table
Syntax:
UPDATE [ ONLY ] table SET col = expression [, ...]
[ FROM fromlist ]
[ WHERE condition ]

So try:

update nodes set parent_id=n2.id FROM nodes n2 where
n2.key=nodes.parent_id;

Unfortunatly you can't alias the table you're
updating, but you can alias
the rest.
--
Martijn van Oosterhout <kl*****@svana.org>
http://svana.org/kleptog/

(... have gone from d-i being barely usable even

by its developers

anywhere, to being about 20% done. Sweet. And the

last 80% usually takes

20% of the time, too, right?) -- Anthony Towns,

debian-devel-announce

ATTACHMENT part 2 application/pgp-signature

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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match

[scott.marlowe]

On Fri, 13 Feb 2004, CSN wrote:

That does the trick. I'd also like to figure out a way
to set all parent_ids to NULL if no parent row can be
found. I haven't been able to figure it out so far.

could a circular foreign key reference with one delete set null type thing
work? then it'd be automagic
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