Enum Volatility 

pub enum Volatility {
    Immutable,
    Stable,
    Volatile,
}

How a function’s output changes with respect to a fixed input

The volatility of a function determines eligibility for certain optimizations. You should always define your function to have the strictest possible volatility to maximize performance and avoid unexpected results.

Variants

Immutable

Always returns the same output when given the same input.

DataFusion will inline immutable functions during planning.

For example, the abs function is immutable, so abs(-1) will be evaluated and replaced with 1 during planning rather than invoking the function at runtime.

Stable

May return different values given the same input across different queries but must return the same value for a given input within a query.

For example, the now() function is stable, because the query select col1, now() from t1, will return different results each time it is run, but within the same query, the output of the now() function has the same value for each output row.

DataFusion will inline Stable functions when possible. For example, Stable functions are inlined when planning a query for execution, but not in View definitions or prepared statements.

Volatile

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 on different rows. An example of this is the random() function.

DataFusion can not evaluate such functions during planning or push these predicates into scans. 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 duplicate 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

Formats the value using the given formatter.

impl Hash for Volatility

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

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