带修饰符的SQL平均值

Question

I have a following data in my Oracle SQL database:

VALUE   CURRENCY
143.88  PLN
440     PLN
21      USD
210.46  PLN
104.17  CHF
324.5   USD
198.84  PLN

What I want to do is to calculate an average value taking into account there are different currencies. What is the easiest method to do this?

Right now I'm creating multiple columns with all desired values, but I have a problem with choosing right value according to currency in particular row.

SELECT VALUE,VALUE*3.08,VALUE*3.37,CURRENCY
  FROM DATA_SAMPLE
    WHERE VALUE IS NOT NULL

Answer 1

Lets keep it normalised, for easy querying. Have 2 tables Say,

Price (CurrencyCode,Value)

And

Currency_Conversion(CurrencyCode, CurrencyName,conversion_factor)

Price:

VALUE   CURRENCYCODE
143.88  PLN
440     PLN
21      USD
210.46  PLN
104.17  CHF
324.5   USD
198.84  PLN

Currency_Conversion:

CURRENCYCODE CONVFACTOR
PLN          3.08
USD          1
CHF          3.37

Query:

SELECT CONV.CURRENCYCODE , AVG(PRICE.VALUE * CONV. CONVFACTOR) as VALUE
FROM PRICE, CURRENCY_CONVERSION CONV
WHERE
     PRICE. CURRENCYCODE = CONV. CURRENCYCODE
GROUP BY
     CONV. CURRENCYCODE

Answer 2

I would go with the lookup table solution, but if you can't do that, here is a query that may help you.

SELECT
  case
    when currency = 'USD' then value*2.1
    when currency = 'PLN' then value*[INSERT PLN CURRENCY HERE]
  end
FROM DATA_SAMPLE
WHERE VALUE IS NOT NULL

Answer 3

I would write function which takes currency code and returns current conversion rate. Then I would use this function to normalize values - convert them into one currency. Then I would calculate average.

Kind of pseudo sql (I'm not Oracle expert :))

CREATE FUNCTION FunctionConvertCurrency
...

SELECT AVG(VALUE*FunctionConvertCurrency(CURRENCY))
FROM DATA_SAMPLE

Answer 4

Create a table with currency prices. Let's say PRICES with columns CURRENCY and PRICE . Then select the average value:

SELECT avg(ds.value*p.price) FROM data_sample ds JOIN prices p ON ds.currency = p.currency WHERE ds.value is not null;