Problem with creating a collection from query

Question

This is driving me nuts. What I am trying to do is create a collection but the sql to create it is produced dynamically. The query I want to end up with in this example is -
select pr.code,pr.description, max(decode(pe.period_beginning,'01-NOV-08',fe.effort,0)) NOV_08,1 NOV_08_PERIOD_ID, max(decode(pe.period_beginning,'01-DEC-08',fe.effort,0)) DEC_08,21 DEC_08_PERIOD_ID, max(decode(pe.period_beginning,'01-JAN-09',fe.effort,0)) JAN_09,22 JAN_09_PERIOD_ID, max(decode(pe.period_beginning,'01-FEB-09',fe.effort,0)) FEB_09,41 FEB_09_PERIOD_ID, max(decode(pe.period_beginning,'01-MAR-09',fe.effort,0)) MAR_09,81 MAR_09_PERIOD_ID from forecast_projects pr,forecast_periods pe,forecast_effort fe
where pr.id=fe.project_id(+)
and pe.id(+)=fe.period_id group by pr.code,pr.description order by pr.code
but the list of dates within single quotes are derived from some pl/sql which pulls them from a table.
So my pl/sql looks like this -
begin
if apex_collection.collection_exists(p_collection_name=>'KEANEFORECAST') then
apex_collection.delete_collection(p_collection_name=>'KEANEFORECAST');
end if;
declare
l_period date;
l_period_id number := 0;
l_query varchar2(1400) := '';
l_query_start varchar2(1400) := 'select pr.code,pr.description,';
l_query_part1 varchar2(1400) := ' max(decode(pe.period_beginning,''';
l_query_part2 varchar2(1400) := ''',fe.effort,0)) ';
l_query_end varchar2(1400) := ' from forecast_projects pr,forecast_periods pe,forecast_effort fe
where pr.id=fe.project_id(+)
and pe.id(+)=fe.period_id group by pr.code,pr.description order by pr.code';
begin
for c1 in (
select id,period_beginning into l_period_id,l_period
from forecast_periods order by 1) loop
l_query := l_query || l_query_part1 || c1.period_beginning || l_query_part2 ||
replace(substr(c1.period_beginning,4),'-','_') || ',' || c1.id || ' ' ||
replace(substr(c1.period_beginning,4),'-','_') || '_PERIOD_ID,';
end loop;
l_query := substr(l_query,0,length(l_query)-1);
l_query := l_query_start || l_query || l_query_end;
dbms_output.put_line(l_query);
apex_collection.create_collection_from_query(
p_collection_name=>'KEANEFORECAST',
p_query=> l_query);
end;
end;
Now what happens is that the query is produced perfectly - the dbms_output.put_line gives me the exact query as quoted at the top of my posting, and if I run it I get the desired results. If I run this whole block of pl/sql it also works absolutely fine and my collection is created - great.
However if I put this pl/sql into an onLoad Before Header block then when I try to run the page I get the following -
ORA-20104: create_collection_from_query Error:ORA-20104: create_collection_from_query ParseErr:ORA-00923: FROM keyword not found where expected
I think it is getting in a mess with the quotes in the query, but I do not know why and I have been racking my brains to think of a workaround. It's odd that it works fine if I run it standalone in the SQL Commands tab but not as a page process.
I'd be really grateful for any advice/pointers here.
Thanks in advance.

Answer 1

You are an absolute star - thank you! What this enabled me to do was to see the query being produced - which was showing it different to that which dbms_output.put_line reported - no idea why this should be. Anyway this allowed me to correct a couple of things which then enabled it all to work.
The thing that showed as different was the representation of a date field - dbms_output.put_Line was showing this in DD-MON-YYYY format whereas the debug showed it with a timestamp portion.
Thank you again.