[SQL] extend INSERT by 'INSERT INTO table FETCH ... FROM cursor' syntax

[Alexander Vlasenko]

Please CC me, I am not subscribed.

An imaginary SQL statement
INSERT INTO table FETCH ... FROM cursor;
looks almost the same as currently available
INSERT INTO table SELECT ...;

I tried it because I needed to insert a row in a table
after I DELETEd a set of rows, something like this:

BEGIN;
DECLARE total CURSOR
 FOR SELECT 
  SUBSTR(datetime,1,7)||'-01 00:00:00' as month,
  client,
  SUM(money)
 FROM stat
 WHERE SUBSTR(datetime,1,7)='2003-10'
 GROUP BY month,client;
DELETE FROM stat WHERE SUBSTR(datetime,1,7)='2003-10';
INSERT INTO stat FETCH ALL FROM total;
COMMIT;

but it does not work, chokes on FETCH ALL.

I want to sum up all the money by month, delete all the rows
(possibly thousands of them) and insert one row per client
with monthly totals.

Obviously I cannot swap order of INSERT and DELETE here.

I hesitate to post this to [EMAIL PROTECTED],
do I have to? ;)

-- 
Alexander Vlasenko

---(end of broadcast)---
TIP 8: explain analyze is your friend

Re: [SQL] extend INSERT by 'INSERT INTO table FETCH ... FROM cursor' syntax

[Alexander Vlasenko]

On Monday 27 October 2003 21:35, Josh Berkus wrote:
> Alexander,
>
> > > BEGIN;
> > > DECLARE total CURSOR
> > >  FOR SELECT=20
> > >   SUBSTR(datetime,1,7)||'-01 00:00:00' as month,
> > >   client,
> > >   SUM(money)
> > >  FROM stat
> > >  WHERE SUBSTR(datetime,1,7)=3D'2003-10'
> > >  GROUP BY month,client;
> > > DELETE FROM stat WHERE SUBSTR(datetime,1,7)=3D'2003-10';
> > > INSERT INTO stat FETCH ALL FROM total;
> > > COMMIT;

[ BTW: quoted-printable is evil ;) ]

> > >
> > > but it does not work, chokes on FETCH ALL.
>
> Well, there's two problems with your program:
>
> 1) INSERT INTO  FETCH ALL is not currently implemented.  You would need
> to use a loop, and insert one row at a time by value.

Exactly. I was saying that if implemented it may be useful.
My example is certainly doable without it but it quickly gets ugly
since I can't use this nifty trick.

> 2) You can't insert the rows you've just deleted from the base tables.  In
> your example, the TOTAL cursor would be empty.   I think that what you
> really want is a temp table.

Why do you think it would be empty? It is not. I tried this:

BEGIN;
DECLARE total CURSOR
 FOR SELECT
  SUBSTR(datetime,1,7)||'-01 00:00:00' as month,
  client,
  SUM(money)
 FROM stat
 WHERE SUBSTR(datetime,1,7)='2003-10'
 GROUP BY month,client;
DELETE FROM stat WHERE SUBSTR(datetime,1,7)='2003-10';
FETCH ALL FROM total;   <===
COMMIT;

and it does work as expected. FETCH spews out already deleted rows.
There is no problem with it.
-- 
Alexander Vlasenko

---(end of broadcast)---
TIP 6: Have you searched our list archives?

   http://archives.postgresql.org

[SQL] unsubscribe

[Alexander Vlasenko]

unsubscribe


---(end of broadcast)---
TIP 4: Don't 'kill -9' the postmaster