2010YOUY01 commented on code in PR #7726:
URL: https://github.com/apache/arrow-datafusion/pull/7726#discussion_r1343054607
##########
datafusion/expr/src/signature.rs:
##########
@@ -20,35 +20,77 @@
use arrow::datatypes::DataType;
+/// Constant that is used as a placeholder for any valid timezone.
+/// This is used where a function can accept a timestamp type with any
+/// valid timezone, it exists to avoid the need to enumerate all possible
+/// timezones. See [`TypeSignature`] for more details.
+///
+/// Type coercion always ensures that functions will be executed using
+/// timestamp arrays that have a valid time zone. Functions must never
+/// return results with this timezone.
+pub const TIMEZONE_WILDCARD: &str = "+TZ";
+
///A function's volatility, which defines the functions eligibility for
certain optimizations
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]
pub enum Volatility {
- /// Immutable - An immutable function will always return the same output
when given the same
- /// input. An example of this is [super::BuiltinScalarFunction::Cos].
+ /// An immutable function will always return the same output when given
the same
+ /// input. An example of this is [super::BuiltinScalarFunction::Cos].
DataFusion
+ /// will attempt to inline immutable functions during planning.
Immutable,
- /// Stable - A stable function may return different values given the same
input across different
+ /// 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 [super::BuiltinScalarFunction::Now].
+ /// this is [super::BuiltinScalarFunction::Now]. DataFusion
+ /// will attempt to inline immutable functions during planning, when
possible.
Stable,
- /// Volatile - A volatile function may change the return value from
evaluation to evaluation.
+ /// 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
[super::BuiltinScalarFunction::Random].
+ /// same query. An example of this is
[super::BuiltinScalarFunction::Random]. DataFusion
+ /// can not evaluate such functions during planning.
Review Comment:
```suggestion
/// 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.
```
##########
datafusion/expr/src/signature.rs:
##########
@@ -20,35 +20,77 @@
use arrow::datatypes::DataType;
+/// Constant that is used as a placeholder for any valid timezone.
+/// This is used where a function can accept a timestamp type with any
+/// valid timezone, it exists to avoid the need to enumerate all possible
+/// timezones. See [`TypeSignature`] for more details.
+///
+/// Type coercion always ensures that functions will be executed using
+/// timestamp arrays that have a valid time zone. Functions must never
+/// return results with this timezone.
+pub const TIMEZONE_WILDCARD: &str = "+TZ";
+
///A function's volatility, which defines the functions eligibility for
certain optimizations
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]
pub enum Volatility {
- /// Immutable - An immutable function will always return the same output
when given the same
- /// input. An example of this is [super::BuiltinScalarFunction::Cos].
+ /// An immutable function will always return the same output when given
the same
+ /// input. An example of this is [super::BuiltinScalarFunction::Cos].
DataFusion
+ /// will attempt to inline immutable functions during planning.
Immutable,
- /// Stable - A stable function may return different values given the same
input across different
+ /// 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 [super::BuiltinScalarFunction::Now].
+ /// this is [super::BuiltinScalarFunction::Now]. DataFusion
+ /// will attempt to inline immutable functions during planning, when
possible.
Review Comment:
```suggestion
/// 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.
```
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