Oracle9i SQL Reference Release 1 (9.0.1) Part Number A9012501 

Functions, 23 of 166
corr::=
corr
CORR
returns the coefficient of correlation of a set of number pairs. You can use it as an aggregate or analytic function.
Both expr1 and expr2 are number expressions. Oracle applies the function to the set of (expr1 , expr2) after eliminating the pairs for which either expr1 or expr2 is null. Then Oracle makes the following computation:
COVAR_POP(expr1, expr2) / (STDDEV_POP(expr1) * STDDEV_POP(expr2))
The function returns a value of type NUMBER
. If the function is applied to an empty set, it returns null.
The following example calculates the coefficient of correlation between the list prices and minimum prices of products by weight class in the sample view oe.products
:
SELECT weight_class, CORR(list_price, min_price) FROM products GROUP BY weight_class; WEIGHT_CLASS CORR(LIST_PRICE,MIN_PRICE)   1 .99914795 2 .999022941 3 .998484472 4 .999359909 5 .999536087
The following example returns the cumulative coefficient of correlation of monthly sales revenues and monthly units sold from the sample tables sh.sales
and sh.times
for year 1998:
SELECT t.calendar_month_number, CORR (SUM(s.amount_sold), SUM(s.quantity_sold)) OVER (ORDER BY t.calendar_month_number) as CUM_CORR FROM sales s, times t WHERE s.time_id = t.time_id AND calendar_year = 1998 GROUP BY t.calendar_month_number ORDER BY t.calendar_month_number; CALENDAR_MONTH_NUMBER CUM_CORR   1 2 1 3 .994309382 4 .852040875 5 .846652204 6 .871250628 7 .910029803 8 .917556399 9 .920154356 10 .86720251 11 .844864765 12 .903542662
Correlation functions require more than one row on which to operate, so the first row in the preceding example has no value calculated for it.

Copyright © 19962001, Oracle Corporation. All Rights Reserved. 
