Trait datafusion::logical_expr::ScalarUDFImpl
source · pub trait ScalarUDFImpl: Debug + Send + Sync {
// Required methods
fn as_any(&self) -> &(dyn Any + 'static);
fn name(&self) -> &str;
fn signature(&self) -> &Signature;
fn return_type(
&self,
arg_types: &[DataType]
) -> Result<DataType, DataFusionError>;
fn invoke(
&self,
_args: &[ColumnarValue]
) -> Result<ColumnarValue, DataFusionError>;
// Provided methods
fn return_type_from_exprs(
&self,
_args: &[Expr],
_schema: &dyn ExprSchema,
arg_types: &[DataType]
) -> Result<DataType, DataFusionError> { ... }
fn invoke_no_args(
&self,
_number_rows: usize
) -> Result<ColumnarValue, DataFusionError> { ... }
fn aliases(&self) -> &[String] { ... }
fn monotonicity(&self) -> Result<Option<Vec<Option<bool>>>, DataFusionError> { ... }
fn simplify(
&self,
args: Vec<Expr>,
_info: &dyn SimplifyInfo
) -> Result<ExprSimplifyResult, DataFusionError> { ... }
fn short_circuits(&self) -> bool { ... }
}Expand description
Trait for implementing ScalarUDF.
This trait exposes the full API for implementing user defined functions and can be used to implement any function.
See advanced_udf.rs for a full example with complete implementation and
ScalarUDF for other available options.
§Basic Example
#[derive(Debug)]
struct AddOne {
signature: Signature
};
impl AddOne {
fn new() -> Self {
Self {
signature: Signature::uniform(1, vec![DataType::Int32], Volatility::Immutable)
}
}
}
/// Implement the ScalarUDFImpl trait for AddOne
impl ScalarUDFImpl for AddOne {
fn as_any(&self) -> &dyn Any { self }
fn name(&self) -> &str { "add_one" }
fn signature(&self) -> &Signature { &self.signature }
fn return_type(&self, args: &[DataType]) -> Result<DataType> {
if !matches!(args.get(0), Some(&DataType::Int32)) {
return plan_err!("add_one only accepts Int32 arguments");
}
Ok(DataType::Int32)
}
// The actual implementation would add one to the argument
fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> { unimplemented!() }
}
// Create a new ScalarUDF from the implementation
let add_one = ScalarUDF::from(AddOne::new());
// Call the function `add_one(col)`
let expr = add_one.call(vec![col("a")]);Required Methods§
sourcefn signature(&self) -> &Signature
fn signature(&self) -> &Signature
Returns the function’s Signature for information about what input
types are accepted and the function’s Volatility.
sourcefn return_type(
&self,
arg_types: &[DataType]
) -> Result<DataType, DataFusionError>
fn return_type( &self, arg_types: &[DataType] ) -> Result<DataType, DataFusionError>
What DataType will be returned by this function, given the types of
the arguments.
§Notes
If you provide an implementation for Self::return_type_from_exprs,
DataFusion will not call return_type (this function). In this case it
is recommended to return DataFusionError::Internal.
sourcefn invoke(
&self,
_args: &[ColumnarValue]
) -> Result<ColumnarValue, DataFusionError>
fn invoke( &self, _args: &[ColumnarValue] ) -> Result<ColumnarValue, DataFusionError>
Invoke the function on args, returning the appropriate result
The function will be invoked passed with the slice of ColumnarValue
(either scalar or array).
If the function does not take any arguments, please use invoke_no_args instead and return not_impl_err for this function.
§Performance
For the best performance, the implementations of invoke should handle
the common case when one or more of their arguments are constant values
(aka ColumnarValue::Scalar).
ColumnarValue::values_to_arrays can be used to convert the arguments
to arrays, which will likely be simpler code, but be slower.
Provided Methods§
sourcefn return_type_from_exprs(
&self,
_args: &[Expr],
_schema: &dyn ExprSchema,
arg_types: &[DataType]
) -> Result<DataType, DataFusionError>
fn return_type_from_exprs( &self, _args: &[Expr], _schema: &dyn ExprSchema, arg_types: &[DataType] ) -> Result<DataType, DataFusionError>
What DataType will be returned by this function, given the
arguments?
Note most UDFs should implement Self::return_type and not this
function. The output type for most functions only depends on the types
of their inputs (e.g. sqrt(f32) is always f32).
By default, this function calls Self::return_type with the
types of each argument.
This method can be overridden for functions that return different types based on the values of their arguments.
For example, the following two function calls get the same argument
types (something and a Utf8 string) but return different types based
on the value of the second argument:
arrow_cast(x, 'Int16')–>Int16arrow_cast(x, 'Float32')–>Float32
§Notes:
This function must consistently return the same type for the same
logical input even if the input is simplified (e.g. it must return the same
value for ('foo' | 'bar') as it does for (‘foobar’).
sourcefn invoke_no_args(
&self,
_number_rows: usize
) -> Result<ColumnarValue, DataFusionError>
fn invoke_no_args( &self, _number_rows: usize ) -> Result<ColumnarValue, DataFusionError>
Invoke the function without args, instead the number of rows are provided,
returning the appropriate result.
sourcefn aliases(&self) -> &[String]
fn aliases(&self) -> &[String]
Returns any aliases (alternate names) for this function.
Aliases can be used to invoke the same function using different names.
For example in some databases now() and current_timestamp() are
aliases for the same function. This behavior can be obtained by
returning current_timestamp as an alias for the now function.
Note: aliases should only include names other than Self::name.
Defaults to [] (no aliases)
sourcefn monotonicity(&self) -> Result<Option<Vec<Option<bool>>>, DataFusionError>
fn monotonicity(&self) -> Result<Option<Vec<Option<bool>>>, DataFusionError>
This function specifies monotonicity behaviors for User defined scalar functions.
sourcefn simplify(
&self,
args: Vec<Expr>,
_info: &dyn SimplifyInfo
) -> Result<ExprSimplifyResult, DataFusionError>
fn simplify( &self, args: Vec<Expr>, _info: &dyn SimplifyInfo ) -> Result<ExprSimplifyResult, DataFusionError>
Optionally apply per-UDF simplification / rewrite rules.
This can be used to apply function specific simplification rules during
optimization (e.g. arrow_cast –> Expr::Cast). The default
implementation does nothing.
Note that DataFusion handles simplifying arguments and “constant
folding” (replacing a function call with constant arguments such as
my_add(1,2) --> 3 ). Thus, there is no need to implement such
optimizations manually for specific UDFs.
§Arguments
- ‘args’: The arguments of the function
- ‘schema’: The schema of the function
§Returns
ExprSimplifyResult indicating the result of the simplification NOTE
if the function cannot be simplified, the arguments MUST be returned
unmodified
sourcefn short_circuits(&self) -> bool
fn short_circuits(&self) -> bool
Returns true if some of this exprs subexpressions may not be evaluated
and thus any side effects (like divide by zero) may not be encountered
Setting this to true prevents certain optimizations such as common subexpression elimination
Implementors§
impl ScalarUDFImpl for ArrowCastFunc
impl ScalarUDFImpl for ArrowTypeOfFunc
impl ScalarUDFImpl for CoalesceFunc
impl ScalarUDFImpl for GetFieldFunc
impl ScalarUDFImpl for NamedStructFunc
impl ScalarUDFImpl for NullIfFunc
impl ScalarUDFImpl for NVL2Func
impl ScalarUDFImpl for NVLFunc
impl ScalarUDFImpl for StructFunc
impl ScalarUDFImpl for DigestFunc
impl ScalarUDFImpl for Md5Func
impl ScalarUDFImpl for SHA224Func
impl ScalarUDFImpl for SHA256Func
impl ScalarUDFImpl for SHA384Func
impl ScalarUDFImpl for SHA512Func
impl ScalarUDFImpl for CurrentDateFunc
Create an implementation of current_date() that always returns the
specified current date.
The semantics of current_date() require it to return the same value
wherever it appears within a single statement. This value is
chosen during planning time.
impl ScalarUDFImpl for CurrentTimeFunc
Create an implementation of current_time() that always returns the
specified current time.
The semantics of current_time() require it to return the same value
wherever it appears within a single statement. This value is
chosen during planning time.
impl ScalarUDFImpl for DateBinFunc
impl ScalarUDFImpl for DatePartFunc
impl ScalarUDFImpl for DateTruncFunc
impl ScalarUDFImpl for FromUnixtimeFunc
impl ScalarUDFImpl for MakeDateFunc
impl ScalarUDFImpl for NowFunc
Create an implementation of now() that always returns the
specified timestamp.
The semantics of now() require it to return the same value
wherever it appears within a single statement. This value is
chosen during planning time.
impl ScalarUDFImpl for ToCharFunc
impl ScalarUDFImpl for ToDateFunc
impl ScalarUDFImpl for ToTimestampFunc
to_timestamp SQL function
Note: to_timestamp returns Timestamp(Nanosecond) though its arguments are interpreted as seconds.
The supported range for integer input is between -9223372037 and 9223372036.
Supported range for string input is between 1677-09-21T00:12:44.0 and 2262-04-11T23:47:16.0.
Please use to_timestamp_seconds for the input outside of supported bounds.