COVAR_SAMP

COVAR_SAMP

Syntax covar_samp::=

OVER ( analytic_clause )

COVAR_SAMP ( expr1 , expr2 )

See Also: "Analytic Functions" on page 6-10 for information on syntax, semantics, and restrictions

Purpose

COVAR_SAMP returns the sample covariance 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) pairs after eliminating all pairs for which either expr1 or expr2 is null. Then Oracle makes the following computation:

(SUM(expr1 * expr2) - SUM(expr1) * SUM(expr2) / n) / (n-1)

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COVAR_SAMP

where n is the number of (expr1, expr2) pairs where neither expr1 nor expr2 is null.

The function returns a value of type NUMBER. If the function is applied to an empty set, then it returns null.

See Also:

■"Aggregate Functions" on page 6-8

■"About SQL Expressions" on page 4-2 for information on valid forms of expr

Aggregate Example

The following example calculates the population covariance for the sales revenue amount and the units sold for each year from the sample table sh.sales:

SELECT t.calendar_month_number,

COVAR_POP(s.amount_sold, s.quantity_sold) AS covar_pop, COVAR_SAMP(s.amount_sold, s.quantity_sold) AS covar_samp FROM sales s, times t

WHERE s.time_id = t.time_id AND t.calendar_year = 1998

GROUP BY t.calendar_month_number;

Analytic Example

The following example calculates cumulative sample covariance of the list price and minimum price of the products in the sample schema oe:

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COVAR_SAMP

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CUME_DIST

CUME_DIST

Aggregate Syntax cume_dist_aggregate::=

Analytic Syntax cume_dist_analytic::=

See Also: "Analytic Functions" on page 6-10 for information on syntax, semantics, and restrictions

Purpose

CUME_DIST calculates the cumulative distribution of a value in a group of values. The range of values returned by CUME_DIST is >0 to <=1. Tie values always evaluate to the same cumulative distribution value.

■As an aggregate function, CUME_DIST calculates, for a hypothetical row R identified by the arguments of the function and a corresponding sort specification, the relative position of row R among the rows in the aggregation group. Oracle makes this calculation as if the hypothetical row R were inserted into the group of rows to be aggregated over. The arguments of the function identify a single hypothetical row within each aggregate group. Therefore, they must all evaluate to constant expressions within each aggregate group. The constant argument expressions and the expressions in the ORDER BY clause of the aggregate match by position. Therefore, the number of arguments must be the same and their types must be compatible.

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CUME_DIST

■As an analytic function, CUME_DIST computes the relative position of a specified value in a group of values. For a row R, assuming ascending ordering, the CUME_DIST of R is the number of rows with values lower than or equal to the value of R, divided by the number of rows being evaluated (the entire query result set or a partition).

Aggregate Example

The following example calculates the cumulative distribution of a hypothetical employee with a salary of $15,500 and commission rate of 5% among the employees in the sample table oe.employees:

SELECT CUME_DIST(15500, .05) WITHIN GROUP

(ORDER BY salary, commission_pct) "Cume-Dist of 15500" FROM employees;

Cume-Dist of 15500

------------------

.972222222

Analytic Example

The following example calculates the salary percentile for each employee in the purchasing area. For example, 40% of clerks have salaries less than or equal to Himuro.

SELECT job_id, last_name, salary, CUME_DIST()

OVER (PARTITION BY job_id ORDER BY salary) AS cume_dist FROM employees

WHERE job_id LIKE ’PU%’;

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