VAR_SAMP is an aggregate function that evaluates the sample variance of an expression over a set of rows.
See Aggregates (set functions) for more information about these functions.
VAR_SAMP is allowed only on expressions that evaluate to numeric data types.
VAR_SAMP ( expression )
The expression can contain multiple column references or expressions, but it cannot contain another aggregate or subquery. It must evaluate to a built-in numeric data type. If an expression evaluates to NULL, the aggregate skips that value.
The resulting data type is DOUBLE (it might overflow).
Sample variance is calculated as follows:
[ sum(xi2) - sum(xi)2/n ]/(n-1) where n is the number of items in the population x1 ... xn are the items in the population
-- find the sample variance in flight time per aircraft SELECT AIRCRAFT, VAR_SAMP( flying_time ) FROM flights GROUP BY aircraft;