STDDEV_POP is an aggregate function that evaluates the
standard deviation of an expression over a population.

See Aggregates (set functions) for more
information about these functions.

STDDEV_POP is allowed only on expressions that evaluate to numeric data
types.

## Syntax

**STDDEV_POP ( ***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).

## Example

**-- find the standard deviation in flight time per aircraft
SELECT AIRCRAFT, STDDEV_POP( flying_time )
FROM flights GROUP BY aircraft;
**