Thread: extend INSERT by 'INSERT INTO table FETCH ... FROM cursor' syntax

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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 pgsql-hackers@postgresql.org,
do I have to? ;)

--
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=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;
> 
> 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 pgsql-hackers@postgresql.org,
> do I have to? ;)
> 
> --=20
> Alexander Vlasenko
> 
Using a temporary table to buffer the result comes to mind. 
Regards, Christoph 

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;
> >
> > 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.

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.

--
-Josh BerkusAglio Database SolutionsSan Francisco

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 CURSORFOR SELECT SUBSTR(datetime,1,7)||'-01 00:00:00' as month, client, SUM(money)FROM statWHERE
SUBSTR(datetime,1,7)='2003-10'GROUPBY 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