sql task. sos plz!

[Moonlight]

Description of the application. The following relational schema is used to maintain stock
price information.
stocks (skey, issued)

For each stock in the database, a unique identifier (skey, data type varchar2(10)) and
the date the stock was issued (issued, data type date) is stored.

stockdev (skey, tdate, price)

This table stores the time series of the diferent stock prices. For each stock referenced
by skey and trading day (tdate, data type date) the price (price, data type number)
is stored.

Compute the covariance of the time series of the stocks 'oracle' and 'ibm'.
Hint: In order to compute the covariance of two random variables you may use the
formula cov(X; Y ) = E(X
Y )
---------------------------
i got some ideas, but noth comes out

SELECT (SUM ( x * y ) - SUM ( y ) * SUM ( x ) * SUM ( x ) / n) / n

FROM stockdev
where ....?

but duno how to tell, that x is skey "oracle'-s price & y - ibm's. price1, price2??

was hinted to put subqueries into the cov formula:

SELECT (SUM (select price from stockdev where skey='oracle' AND tdate BETWEEN issuedate AND ??

or group by tdate?

how to tell that it's time series & not 1
can one say MAX(date) meaning the last date?
no, you should sort in order to get last date
Silence (07:37 PM) :
nasty.. group by won't do?\

[Moonlight]

Originally Posted by accemic26

что есть студентка у которой 4-е мажера ?

accemic, ti ne verish v moe real'no sushetvovanie na Zemle? spustis' s Luni

Obelix jan, senks! no examen 4 chisa nazad sdala) nikakix php codes toli qsl queries, moi mozgi perekluchilis' uje na preis- und allokationstheorie:P

[Obelix]

)

Кстати, можно один неприличный вопрос я вот долго пытаюсь понять на чего это ты учишся и никак не пойму

[Moonlight]

oy dumaesh ya ponimayu? int'l masters' prog takaya, chtob poluchit 1 degree, nado min 3, max 4 majors zakonchit'. ideya po idee super, tol'ko organizovali xrenovo, studenti libo muchayut'ca, lubo radi vozmojnosti jit' v berline i zakanchivayut' za 6 let pripevayushi vmesto obichnogo 2-yr masters.

look http://www.wiwi.hu-berlin.de/mems/
iz 3 fields of spec doljni vibrat' min 1 major s kajdogo. tk kak v yerevane uje got kibernetik-ekonomist, a eto po suti soderjit i Econometric Methods, i Multivariate Statistical Analysis, i
Operations Research. so ot Quantitative Methods dla menya novoe tol'ko Information Systems, chto i vibrala kak 1 mojor. i esho u mya Entrepreneurship, Finance and Banking, Advanced Microeconomic Analysis. esli vijit', potom budet kruto..

kstati, accemik, esli ti esho tut, ves'ma rekomenduyu te. s MEMS u te ne ostanet'ca nikakoy otrecatel'noy energii /i ne tol'ko otrecatel'noy/ chtob na golovu forumchan izlit', da i ne budet u te stol'ko vremeni na forum:P

[Moonlight]

a vaashe, vse eto fignya. moe prizvanie- psixolog