VAR_POP

Syntax

var_pop::=
Description of var_pop.gif follows

Description of the illustration var_pop.gif

See Also:

"Analytic Functions " for information on syntax, semantics, and restrictions

Purpose

VAR_POP returns the population variance of a set of numbers after discarding the nulls in this set. You can use it as both an aggregate and analytic function.

This function takes as an argument any numeric datatype or any nonnumeric datatype that can be implicitly converted to a numeric datatype. The function returns the same datatype as the numeric datatype of the argument.

See Also:

Table 2-11, "Implicit Type Conversion Matrix" for more information on implicit conversion

If the function is applied to an empty set, then it returns null. The function makes the following calculation:

(SUM(expr2) - SUM(expr)2 / COUNT(expr)) / COUNT(expr)

See Also:

"About SQL Expressions " for information on valid forms of expr and "Aggregate Functions "

Aggregate Example

The following example returns the population variance of the salaries in the employees table:

SELECT VAR_POP(salary) FROM employees;

VAR_POP(SALARY)
---------------
     15140307.5

Analytic Example

The following example calculates the cumulative population and sample variances in the sh.sales table of the monthly sales in 1998:

SELECT t.calendar_month_desc,
   VAR_POP(SUM(s.amount_sold)) 
      OVER (ORDER BY t.calendar_month_desc) "Var_Pop",
   VAR_SAMP(SUM(s.amount_sold)) 
      OVER (ORDER BY t.calendar_month_desc) "Var_Samp" 
  FROM sales s, times t
  WHERE s.time_id = t.time_id AND t.calendar_year = 1998
  GROUP BY t.calendar_month_desc;

CALENDAR    Var_Pop   Var_Samp
-------- ---------- ----------
1998-01           0
1998-02  6.1321E+11 1.2264E+12
1998-03  4.7058E+11 7.0587E+11
1998-04  4.6929E+11 6.2572E+11
1998-05  1.5524E+12 1.9405E+12
1998-06  2.3711E+12 2.8453E+12
1998-07  3.7464E+12 4.3708E+12
1998-08  3.7852E+12 4.3260E+12
1998-09  3.5753E+12 4.0222E+12
1998-10  3.4343E+12 3.8159E+12
1998-11  3.4245E+12 3.7669E+12
1998-12  4.8937E+12 5.3386E+12