Re: update help

Forgot to mention that I'm using V6.5. It doesn't seem to like
subqueries, got the following error:

ERROR:  parser: parse error at or near "select"

What I really want to do is follows

t2:    ID    Amount ........-----------------------1    1    ......1    2    ......2    3    ......2    2    ......

and want the following result in t1

t1:    ID    Amount .......-----------------------1    3    ......2    5    ......

Tom Lane wrote:
> 
> Carolyn Wong <carolyn@greatpacific.com.au> writes:
> > I'd like to know what's the correct SQL statement to do the following:
> > update        t1 a
> > set   a.amount = sum(b.amount)
> > from  t2 b
> > where a.id = b.id
> 
> Try
> 
> UPDATE t1 SET amount = (select sum(b.amount) from t2 b WHERE t1.id = b.id);
> 
> Or possibly you want
> 
> UPDATE t1 SET amount = (select sum(b.amount) from t2 b WHERE t1.id = b.id)
> WHERE EXISTS (select * FROM t2 b WHERE t1.id = b.id);
> 
> depending on whether you mean to zero out any t1 rows that have no
> matching rows in t2.  Note that you cannot attach an alias name to the
> target table, you have to use its real name in the subselects.
> 
> There was a thread about this very issue a few months ago, and IIRC
> we decided that an aggregate in an UPDATE doesn't have well-defined
> semantics.  The SQL92 spec explicitly disallows it.  Right now PG will
> take it, but we probably do something pretty surprising :-(
> 
>                         regards, tom lane