Strange query plans, and so different results from a view.

Question

In my database (11g), I have a currency exchange rate table, which contains all currencies and their exchange rate to USD. I need to have a number of different exchange rates - To GBP, EUR, etc...
To accomplish this I have created a view, which has one union statement of all the USD exchange rates, with the same data joined back on itself to give the exchange rates based on their exchange rate to USD - ie: SELECT b1.Date, b1.Currency AS FromCurrency, b2.Currency as ToCurrency, b1.Rate/b2.Rate as Exchange Rate FROM Rates b1, Rates b2 on b1.Date = b2.Date
This view works fine when I query it, and returns the data as I expect.
I have a second view that is joined to this view to give a return of the amount in each currency for reporting. This view seems to work correctly when I narrow down the search requirements and have a small set of data.
The issue I am having is when I query the second view and get it to return all the data. Instead of receiving 4 rows per transaction (I am only interested in 4 exchange rates for display) I typically receive up to 2 rows. The first record is for the conversion to USD, the second record is for the conversion to the supplied currency. The issue is that this exchange rate actually includes the aggregate for all 3 other requested currencies (not the USD).
So instead of getting something like:
Amt RC BC (Amt = Amount, RC = Reporting Currency. BC = Base Currency)
60 GBP GBP
80 EUR GBP
100 USD GBP
1000 ZAR GBP
60 GBP USD
80 EUR USD
100 USD USD
1000 ZAR USD
I get the following set of results:
1140 GBP GBP
100 USD GBP
100 USD USD
Has anyone come accross something similar or have any ideas on how I can resolve this?
Thanks
PS: I can get both sets of results from the same view depending on the filter criteria. Also if I convert the exchange rates into a table, it then returns the correct results as expected.

Answer 1

943081 wrote:
The idea is to seek help in solving the problem. I was hoping that perhaps someone had experienced the same thing - different results for "effectively" the same query:Well, that's the issue... without additional info, it's not clear what issue you were seeing.
SELECT * FROM view WHERE Date = '01 January, 2012'
verse
SELECT * FROM view WHERE Date > '31 December, 2011' ORDER BY DateNow it's a bit clearer. That second query is not "effectively" the same as the first query. If the date column is in DATE format, then you ought to have a to_date() around the date string to explicitly convert it into a date so you can do date-to-date comparisons correctly. Also, DATE datatype stores times as well as dates, so asking for data matching midnight of a specific date is different than asking for data greater than midnight of the previous day.
If the date string is a string, then ... well, the string "31 December 2011" is greater than the string "31 August 2013", despite it being an earlier date. This is why making sure you're using the right datatype for the job is important - a date is different to a string that just happens to contain a date.
DateID
I have no objection to using a Date but always struggle to understand what someone means when they tell me "06/07/2012" - granted if the day is above 12 or the same day and month I don't have a problem - but it still leaves 121 days a year that are confusing. sure, but just because you find outputting the display (or rather, someone else's output) confusing doesn't mean you still shouldn't use the correct datatype. Store things as a date, and you can then output it in whatever format you like. Try doing that with a string or a number.
Don't say it doesn't happen as I got a birthday card from a company in May this year when I have specifically entered my date of birth as being the 5 of a month (name drop down box on their website)!Just because someone else doesn't understand how to work with dates correctly doesn't mean you can't! It's not exactly rocket science, after all!*{;-)