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(x_{i}^{2}) - sum(x_{i})^{2}/n ]/(n-1) where n is the number of items in the population x_{1}... x_{n}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;