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

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 Berkus
Aglio Database Solutions
San 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 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