Stewart Anderson wrote:
Subject: suggestions sought on returning rows from oracle proc and
deleting them in same proc
Hi,
I am hoping someone might have had to do something like this and have
a
good solution. I am using DBD::Oracle. I have a table with a simple
integer and a timestamp:
create mytable (id int, created timestamp);
The integer value may appear more than once and the timestamp is the
timestamp when the row was created (it is actually created via a
trigger). Other procedures write "id"s into the table at indeterminate
times. The perl code wants to select the current distinct values of
the
"id" field, do something with them and then all rows which were
present
when the select was issued need to be deleted (since then more rows
may
have been added which must not be touched).
This is easily achieved if I have two procs:
PROCEDURE get(
pdt OUT mytable.created%TYPE,
pcur OUT SYS_REFCURSOR) AS
BEGIN
pdt := utc_timestamp();
OPEN pcur FOR
SELECT DISTINCT(id) FROM mytable WHERE created <= pdt;
END;
and:
PROCEDURE delete(
pdt IN mytable.created%TYPE,
puid IN mytable.id%TYPE) AS
BEGIN
DELETE FROM mytable WHERE id = puid AND created <= pdt;
END;
Perl calls the first one to get the unique ids and the timestamp used
to
retrieve them, does something with the returned ids and then calls the
second procedure one for each id to delete the rows. It does however,
rely on the timestamp_format as if it is changed to remove
milliseconds
for instance the delete above may fail to find any rows (e.g.
timestamp
used was 2008-10-01 14:20:10.5555 but timestamp format omits the
milliseconds then the timestamp pumped in to the second proc is
2008-10-01 14:20:10). As a result of this problem and it is 2 procs,
this one ruled out.
Ideally I'd like to achieve this in one procedure so I can guarantee
no
matter what happens in the perl the returned rows are deleted from the
table. At first I thought that as the number of distinct ids will not
be
that many I could issue my select, loop through them putting them into
an oracle table type, delete the rows in the real table then return
the
oracle table type to perl. However, DBD::Oracle does not support
returning oracle table/array types other than via piped functions and
as
I found, you cannot issue a delete statement in a piped function e.g.,
the following does not work:
type mytype_t IS table of mytable.id%TYPE NOT NULL;
type mytype_a IS TABLE OF mytable.id%TYPE NOT NULL
INDEX BY BINARY_INTEGER;
FUNCTION f_xxx RETURN mytable_t PIPELINED AS
CURSOR cur(param_dt mytable.created%TYPE)
IS SELECT DISTINCT(id) FROM mytable WHERE
created <= param_dt;
i integer := 1;
dt mytable.created%TYPE;
vu mytable_a;
BEGIN
dt := utc_timestamp();
FOR row in cur(dt) LOOP
vu(i) := row.id;
i := i+1;
END LOOP;
-- following delete generates an error
DELETE FROM mytable where created <= dt;
FOR i in vu.first .. vu.last LOOP
PIPE row(vu(i));
END LOOP;
END;
The problem is returning multiple values from rows in a table back to
perl and simultaneously deleting same rows. It can be achieved if I
introduce a temporary table because the proc can select the rows into
the temp table and delete the selected rows in the original table and
the perl reads the temporary table but we try very hard to avoid
temporary tables.
If DBD::Oracle supported the return of oracle table types this would
be
easy.
Do you actually need to do it simultaneously?
It strikes me that you could do it all in perl.
Prepare your select statement and bind any params
Execture it.
Run through the returned rows adding each to an array.
You now have an array with all the items you need to delete
Prepare delete statement
While array {
Bind param
Delete
}
If you get any DB errors issue the rollback and you can try again.
The DBI docs are very easy to follow.
Stewart
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You are right, you can do it all in perl. However, what I forgot to
mention is the user connected to the database has no select permission
on the tables and so the code needs to be in a proc that runs with
definer rights. None of our perl has any access to the database other
than through procedures and functions in packages with definer rights.
Martin
--
Martin J. Evans
Easysoft Limited
http://www.easysoft.com
