Thread: Inserting a needed record before a select
All,
Hello, I'm new to this list but I'm looking for some information.
What I need to do is to find a way to automallically insert a record if it
doesn'
t exist, prior to a SELECT.
Basically, I'm tracking some information based on date and the client
application when retrieving the information knows will that 'current' is
the record with today's date.
What I'd like is a way of of specifiying that when the SELECT is done,
there will be a check that a record exists for the current date and that if
it doesn't exist, a record will be inserted into the table for the current
date and then the SELECT will return the recors including the newly
inserted one.
What I've tried so far is a function that checks for the record, inserts it
if needed, and then returns a cursor that the client can use, but I was
wondering if there was something more direct. I thought of a RULE but I
don't see that they can do processing that expressive.
Here's an example: mytable contains the date based stats information with
another id. All the stats columns are defaulted so just inserting a new
record with the right id and date is sufficient.
=============
CREATE FUNCTION getdatestats (varchar) RETURNS refcursor AS '
DECLARE
myid ALIAS FOR $1;
today date;
ref refcursor;
dummyrow RECORD;
BEGIN
ref := 'statscursor';
SELECT INTO dummyrow * FROM mytable where id = AND statdate = today;
IF NOT FOUND
INSERT INTO mytable (id, statdate) VALUES (myid, today)
END IF;
OPEN ref for SELECT * FROM mytable WHERE id=myid;
RETURN ref;
END;
' LANGUAGE PLPGSQL
=============
Any other ideas? This works but I was wondering if it was possible to do
it without the client needing to do the transaction/cursor handling
(considering I'm only holding up to 30 days worth of data)
Thanks
Jay O'Connor
On Mon, 14 Apr 2003, Jay O'Connor wrote:
> All,
>
> Hello, I'm new to this list but I'm looking for some information.
>
>
> What I need to do is to find a way to automallically insert a record if it
> doesn'
> t exist, prior to a SELECT.
>
> Basically, I'm tracking some information based on date and the client
> application when retrieving the information knows will that 'current' is
> the record with today's date.
>
> What I'd like is a way of of specifiying that when the SELECT is done,
> there will be a check that a record exists for the current date and that if
> it doesn't exist, a record will be inserted into the table for the current
> date and then the SELECT will return the recors including the newly
> inserted one.
>
> What I've tried so far is a function that checks for the record, inserts it
> if needed, and then returns a cursor that the client can use, but I was
> wondering if there was something more direct. I thought of a RULE but I
> don't see that they can do processing that expressive.
>
> Here's an example: mytable contains the date based stats information with
> another id. All the stats columns are defaulted so just inserting a new
> record with the right id and date is sufficient.
> =============
>
> CREATE FUNCTION getdatestats (varchar) RETURNS refcursor AS '
> DECLARE
> myid ALIAS FOR $1;
> today date;
> ref refcursor;
> dummyrow RECORD;
>
> BEGIN
>
> ref := 'statscursor';
> SELECT INTO dummyrow * FROM mytable where id = AND statdate = today;
> IF NOT FOUND
> INSERT INTO mytable (id, statdate) VALUES (myid, today)
> END IF;
>
> OPEN ref for SELECT * FROM mytable WHERE id=myid;
>
> RETURN ref;
> END;
> ' LANGUAGE PLPGSQL
>
> =============
>
>
> Any other ideas? This works but I was wondering if it was possible to do
> it without the client needing to do the transaction/cursor handling
> (considering I'm only holding up to 30 days worth of data)
You're over halfway there. Now you just need to do it in a trigger.
Basically, in older versions of pgsql, you can change your
function to return an opaque (in 7.3. it's now a trigger type, not sure
about 7.2) and just check every time somebody selects from the table for
the row and stick it in. Then make a trigger on it.
\h create trigger
Command: CREATE TRIGGER
Description: define a new trigger
Syntax:
CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
ON table FOR EACH { ROW | STATEMENT }
EXECUTE PROCEDURE func ( arguments )
So, after you've got a function that returns the right type,
create trigger somename before select on tablename for each statement
execute insertdefaultrow(rowid).
At 11:57 AM 04/14/2003 -0600, scott.marlowe wrote:
>> What I need to do is to find a way to automallically insert a record if it
>> doesn'
>> t exist, prior to a SELECT.
>
>You're over halfway there. Now you just need to do it in a trigger.
>Basically, in older versions of pgsql, you can change your
>function to return an opaque (in 7.3. it's now a trigger type, not sure
>about 7.2) and just check every time somebody selects from the table for
>the row and stick it in. Then make a trigger on it.
>
>\h create trigger
>Command: CREATE TRIGGER
>Description: define a new trigger
>Syntax:
>CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
> ON table FOR EACH { ROW | STATEMENT }
> EXECUTE PROCEDURE func ( arguments )
>
>So, after you've got a function that returns the right type,
>
>create trigger somename before select on tablename for each statement
>execute insertdefaultrow(rowid).
That's what I was thinking but the docs for CREATE TRIGGER say that the
event type can be either INSERT, UPDATE, or DELETE so I didn't think that a
trigger for before a select would work
Thanks
Take care,
Jay
On Mon, 14 Apr 2003, Jay O'Connor wrote:
> At 11:57 AM 04/14/2003 -0600, scott.marlowe wrote:
>
> >> What I need to do is to find a way to automallically insert a record if it
> >> doesn'
> >> t exist, prior to a SELECT.
>
> >
> >You're over halfway there. Now you just need to do it in a trigger.
> >Basically, in older versions of pgsql, you can change your
> >function to return an opaque (in 7.3. it's now a trigger type, not sure
> >about 7.2) and just check every time somebody selects from the table for
> >the row and stick it in. Then make a trigger on it.
> >
> >\h create trigger
> >Command: CREATE TRIGGER
> >Description: define a new trigger
> >Syntax:
> >CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
> > ON table FOR EACH { ROW | STATEMENT }
> > EXECUTE PROCEDURE func ( arguments )
> >
> >So, after you've got a function that returns the right type,
> >
> >create trigger somename before select on tablename for each statement
> >execute insertdefaultrow(rowid).
>
>
> That's what I was thinking but the docs for CREATE TRIGGER say that the
> event type can be either INSERT, UPDATE, or DELETE so I didn't think that a
> trigger for before a select would work
Crap, sorry, you're right. You'll need to use a rule. Rules are simpler
than triggers / functions. They're described in the programmer's guide,
section 13 for 7.3.2.
At 12:27 PM 04/14/2003 -0600, scott.marlowe wrote: >Crap, sorry, you're right. You'll need to use a rule. Rules are simpler >than triggers / functions. They're described in the programmer's guide, >section 13 for 7.3.2. Problem is RULEs don't seem to have the sophistication I need (boolean logic...search for a record and if it doesn't exists, insert it, then re-SELECT on the same table) Take care, Jay
On Mon, 14 Apr 2003, Jay O'Connor wrote: > At 12:27 PM 04/14/2003 -0600, scott.marlowe wrote: > > >Crap, sorry, you're right. You'll need to use a rule. Rules are simpler > >than triggers / functions. They're described in the programmer's guide, > >section 13 for 7.3.2. > > Problem is RULEs don't seem to have the sophistication I need (boolean > logic...search for a record and if it doesn't exists, insert it, then > re-SELECT on the same table) I think it might be doable anyway. Since rules allow where clauses, maybe you could make one that had a where clause to test to see if the row existed and if not then it calls a function to create the row. I'm busy wrestling an import script to the ground right now, but I'll try to see if I can make something like that work when I get a minute.