Обсуждение: update on join ?

Hi,

I'd like to update a table  efficiently  where the relevant select-info 
is in another table that is foreign-linked.

Stupid example. 2 tables:
things (thing_id integer, name varchar(100), color varchar(100))
inventory (item_id integer, thing_fk integer references things 
(thing_id), number)

For some reason I'd want to set the number of every red item to 0.
This inventory doesn't contain the color but the foreign key to the 
other table where the color is found.

I tried

UPDATE  things JOIN inventory ON things.thing_id = inventory.thing_fk
SET number = 0
WHERE color = 'red'

PSQL didn't like the JOIN though.
It works like this:

UPDATE inventory
SET number = 0
WHERE  thing_fk IN (SELECT thing_id FROM things WHERE color = 'red')

It's effective but is it efficient, too?

Regards

Andreas wrote:
> I'd like to update a table  efficiently  where the relevant select-info 
> is in another table that is foreign-linked.
> 
> Stupid example. 2 tables:
> things (thing_id integer, name varchar(100), color varchar(100))
> inventory (item_id integer, thing_fk integer references things 
> (thing_id), number)
> 
> For some reason I'd want to set the number of every red item to 0.
> This inventory doesn't contain the color but the foreign key to the 
> other table where the color is found.
> 
> I tried
> 
> UPDATE  things JOIN inventory ON things.thing_id = inventory.thing_fk
> SET number = 0
> WHERE color = 'red'
> 
> PSQL didn't like the JOIN though.
> It works like this:
> 
> UPDATE inventory
> SET number = 0
> WHERE  thing_fk IN (SELECT thing_id FROM things WHERE color = 'red')
> 
> It's effective but is it efficient, too?


What about:

UPDATE  things, inventory  SET number = 0  WHERE color = 'red'  AND things.thing_id = inventory.thing_fk

--- On Wed, 11/21/07, Andreas <maps.on@gmx.net> wrote:> 
> UPDATE inventory
> SET number = 0
> WHERE  thing_fk IN (SELECT thing_id FROM things WHERE color
> = 'red')

This is a perfectly acceptable ANSI-SQL update statement.

Here is non-ANSI update statement that you are probably after:

UPDATE Inventory  SET number = 0 FROM ThingsWHERE Inventory.thing_fk = Things.thing_id  AND Things.color = 'red';

IIRC, Joe Celko referrers to this syntax as "T-SQL".

Regards,
Richard Broersma Jr.

> I tried
> 
> UPDATE  things JOIN inventory ON things.thing_id = inventory.thing_fk
> SET number = 0
> WHERE color = 'red'
> 

use the cool "from" clause in the update

update things tset number = 0
from inventory i
where t.thing_id = i.thing_fk
and i.color = 'red';



     ____________________________________________________________________________________
Get easy, one-click access to your favorites. 
Make Yahoo! your homepage.
http://www.yahoo.com/r/hs