ORA-01858 error from Apex Report on working/valid underlying query

Question

After two days of searching these forums and AskTom, I think I need to post the following problem.
I have what seems to be a valid view of some data created as follows (with an apology for the formatting - doesn't seem to be a way of using a fixed font here):
CREATE OR REPLACE FORCE VIEW "PRICING_CAPABILITY"."POW_EXEC_SUMM010" ("Item",
"Jul-09", "Aug-09", "Sep-09", "Oct-09", "Nov-09", "Dec-09", "Jan-10",
"Feb-10", "Mar-10", "Apr-10", "May-10", "Jun-10", "YTD")
AS
SELECT
"Item",
SUM(DECODE("ItemMonth",'Jul-09',"ItemValue",0)) "Jul-09",
SUM(DECODE("ItemMonth",'Aug-09',"ItemValue",0)) "Aug-09",
SUM(DECODE("ItemMonth",'Sep-09',"ItemValue",0)) "Sep-09",
SUM(DECODE("ItemMonth",'Oct-09',"ItemValue",0)) "Oct-09",
SUM(DECODE("ItemMonth",'Nov-09',"ItemValue",0)) "Nov-09",
SUM(DECODE("ItemMonth",'Dec-09',"ItemValue",0)) "Dec-09",
SUM(DECODE("ItemMonth",'Jan-10',"ItemValue",0)) "Jan-10",
SUM(DECODE("ItemMonth",'Feb-10',"ItemValue",0)) "Feb-10",
SUM(DECODE("ItemMonth",'Mar-10',"ItemValue",0)) "Mar-10",
SUM(DECODE("ItemMonth",'Apr-10',"ItemValue",0)) "Apr-10",
SUM(DECODE("ItemMonth",'May-10',"ItemValue",0)) "May-10",
SUM(DECODE("ItemMonth",'Jun-10',"ItemValue",0)) "Jun-10",
SUM("ItemValue") AS "YTD"
FROM
SELECT
'New Proposals Received' AS "Item",
TO_CHAR(t1.scope_received,'Mon-RR') AS "ItemMonth",
COUNT(*) AS "ItemValue",
10 AS "SortOrder"
FROM
PRICING_CAPABILITY.POW_DATA t1
WHERE
t1.scope_received IS NOT NULL
AND extract(YEAR FROM t1.scope_received) IN (2009,2010)
AND t1.scope_received >= '01-JUL-2009'
GROUP BY
'New Proposals Received',
TO_CHAR(t1.scope_received,'Mon-RR'),
10
UNION
SELECT
'New Proposals Completed' AS "Item",
TO_CHAR(t2.pricing_approval,'Mon-RR') AS "ItemMonth",
COUNT(*) AS "ItemValue",
20 AS "SortOrder"
FROM
PRICING_CAPABILITY.POW_DATA t1
JOIN PRICING_CAPABILITY.POW_LAST_HISTORY t2
ON
t1.POW_DATA_ID = t2.POW_DATA_ID
WHERE
t2.pricing_approval IS NOT NULL
AND extract(YEAR FROM t2.pricing_approval) IN (2009,2010)
AND t2.pricing_approval >= '01-JUL-2009'
GROUP BY
'New Proposals Completed',
TO_CHAR(t2.pricing_approval,'Mon-RR')
GROUP BY
"Item",
"SortOrder"
ORDER BY
"SortOrder" ;
This view works, ie produces the right results when run (ie select * from ...) in SQL Developer and in the SQL Workshop section of Apex.
But when I attempt to produce an Apex report using it as the source of data, I get the following error:
ORA-01858: a non-numeric character was found where a numeric was expected
The error is displayed before any part of the report itself is displayed, ie the Region Header is displayed and then the error message.
So far, anything I've been able to find on the forums or AskTom suggests that it is probably due to a date conversion problem. But the aim here is to summarise dated records by month, so I'm extracted the year and month elements of the date values, converting them to strings (using TO_CHAR), and then using the resulting 'Mon-YY' strings to group the results.
If there is a better way, I'm interested.
But I don't understand why Apex seems to be rejecting what appear to be valid results from a valid working query.
Any ideas? Suggestions?
Cheers,
Peter

Answer 1

Thanks again, Flavio. I'm learning and I appreciate your patience.
The solution you provided is very similar to the one I came up with after your previous message, but I didn't have the NLS_DATE_LANGUAGE parameter. I'll go back and try it.
I appreciate your explanation re Apex not needing to know and Oracle assuming that the client knows what it is doing, but it puzzles me more.
The way that I originally had things, I think, was consistent with what you have explained, but it didn't work. To make it clear:
1 I had an Oracle view that had no parameters and contained the date literal in the where clause and worked fine in both SQL Developer and in the Apex SQL Workshop.
2 The view did not return any date values. Aside from the column headings and the first column (of character strings), the body of the table comprised integer values only.
3 So, when Apex called the view, I would have expected the Oracle server to independently execute the view and return the (dateless) results to Apex, which would then present the unmodified results in a standard report. This is, I think, what SQL Developer and the Apex SQL Workshop appear to have successfully done.
My expectation seems to be consistent with at least some of your explanation (ie [Oracle assumes] "+that the client knows what it is doing+" and "+apex doesn't need to know anything about the underlying query+"), but is not consistent with actual experience, where Apex seems to know that the underlying query contains a date literal and unsuccessfully (and unnecessarily) attempts to interpret it.
I'm obviously missing something about how Apex and Oracle interact in this situation. While I don't need to know - as I have a working solution now - it is valuable to understand how things work. Makes life easier and more productive.
Cheers,
Peter