Re: UPDATE FROM problem, multiple updates of same row don't seem to work

On Mon, Aug 09, 2004 at 15:16:29 -0500,
David Stanaway <david(at)stanaway(dot)net> wrote:
> Here is an example:
>
> CREATE TABLE tablea(
> id int PRIMARY KEY,
> flag int
> );
>
> CREATE TABLE tableb(
> aid int REFERENCES tablea(id),
> flag int
> );
>
> INSERT INTO tablea VALUES(1,0);
> INSERT INTO tablea VALUES(2,0);
>
> -- Flags for 1st row of tablea - When ORed, should be 7
> INSERT INTO tableb VALUES(1,1);
> INSERT INTO tableb VALUES(1,2);
> INSERT INTO tableb VALUES(1,4);
>
> -- Flags for 2nd row of tablea - When ORed, should be 5
> INSERT INTO tableb VALUES(2,1);
> INSERT INTO tableb VALUES(2,4);
>
>
> UPDATE tablea
> SET flag = tablea.flag | tableb.flag

The original value of tablea.flag for each id will be used here. So that
only one of the tableb.flag values will be or'd in for each id.

> FROM tableb
> WHERE tablea.id = tableb.aid;
>
>
> SELECT * from tablea;
> id | flag
> ----+------
> 1 | 1
> 2 | 1
>
> -- Desired output is
> id | flag
> ----+------
> 1 | 7
> 2 | 5
>
>
> Is there a way around this so that I can get the desired output?

Write a custom aggregate function that does the or for you.