Date: Tue, 15 Jul 2003 14:39:25 +0200
From: Erik Thiele <erik@thiele-hydraulik.de>
To: pgsql-sql@postgresql.org
Subject: Re: summing tables
Message-Id: <20030715143925.54716ed4.erik@thiele-hydraulik.de>
In-Reply-To: <001501c34aca$e70ca280$0600a8c0@fix.ro>
References: <20030715140921.7c5a6a6c.erik@thiele-hydraulik.de>
	<001501c34aca$e70ca280$0600a8c0@fix.ro>
Organization: Thiele-Hydraulik
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On Tue, 15 Jul 2003 15:16:21 +0300
"Viorel Dragomir" <bigchief@vio.ro> wrote:

> update table_name
> set c = a + b + (select c from table_name as x where x.seq = seq-1)
> where c is null;

hmmm. the query is run row by row, isn't it?
but it will have different results depending on the order of those rows.

look, the c value is set by one row-query
and read by the row-query of the row below.

does sql specify some "order is magically always as you expect it" rule?

still i am a little confused.


and i am sorry, i didn't initially specify that the "seq" are not gapless.
i.e. seq-1 does not always exist. but seq-13 could be the next lower one!

zeit=# select * from foo;
 seq | a  | b  | c 
-----+----+----+---
   0 |  1 |  2 | 3
   1 |  1 |  2 |  
   2 |  5 |  7 |  
   3 | -2 | -4 |  
   6 | -1 | -2 |  
   5 | -2 | -2 |  
   4 |  0 |  1 |  
(7 rows)

i created this (gapless for easiness) table and run your query:

zeit=# update foo set c = a + b + (select c from foo as x where x.seq = seq-1) where c is null;
UPDATE 6

#### 6 updates??? really???

zeit=# select * from foo;
 seq | a  | b  | c 
-----+----+----+---
   0 |  1 |  2 | 3
   1 |  1 |  2 |  
   2 |  5 |  7 |  
   3 | -2 | -4 |  
   6 | -1 | -2 |  
   5 | -2 | -2 |  
   4 |  0 |  1 |  
(7 rows)


hmmmm. let's try the statement of the other reply to my initial mail:

UPDATE foo t set c = a + b + (Select c from foo tt where tt.seq = t.seq -1)

zeit=# UPDATE foo t set c = a + b + (Select c from foo tt where tt.seq = t.seq -1);
ERROR:  parser: parse error at or near "t"

hmmmm....

any clues?

cu & thx
erik

> additional checks are required if you want to update c when c is not null
> if all the c are null then this query will do nothing
> > i have a table consisting of 4 integers.
> > 
> > seq is for making the table ordered. (ORDER BY SEQ ASC)
> > a,b,c maybe null
> > 
> > 
> >  seq | a  | b  | c 
> > -----+----+----+---
> >    0 |  1 |  2 | 3
> >    1 |  1 |  2 |  
> >    2 |  5 |  7 |  
> >    3 | -2 | -4 |  
> > 
> > 
> > i am needing a sql statement to do
> > 
> > c=a+b+"the c of the row with seq one less than myself"
> > 
> > this statement has to run over the whole table, in seq order.

-- 
Erik Thiele