Enum Volatility

pub enum Volatility {
    Immutable,
    Stable,
    Volatile,
}

A function’s volatility, which defines the functions eligibility for certain optimizations

Variants

Immutable

An immutable function will always return the same output when given the same input. DataFusion will attempt to inline immutable functions during planning.

Stable

A stable function may return different values given the same input across different queries but must return the same value for a given input within a query. An example of this is the Now function. DataFusion will attempt to inline Stable functions during planning, when possible. For query select col1, now() from t1, it might take a while to execute but now() column will be the same for each output row, which is evaluated during planning.

Volatile

A volatile function may change the return value from evaluation to evaluation. Multiple invocations of a volatile function may return different results when used in the same query. An example of this is the random() function. DataFusion can not evaluate such functions during planning. In the query select col1, random() from t1, random() function will be evaluated for each output row, resulting in a unique random value for each row.

Trait Implementations

impl Clone for Volatility

fn clone(&self) -> Volatility

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Volatility

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Hash for Volatility

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Volatility

fn cmp(&self, other: &Volatility) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Volatility

fn eq(&self, other: &Volatility) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Volatility

fn partial_cmp(&self, other: &Volatility) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Copy for Volatility

impl Eq for Volatility

impl StructuralPartialEq for Volatility