Package io.lenses.sql.udf

Interface UserDefinedAggregateFunction

All Superinterfaces:

UserDefinedFunction

All Known Subinterfaces:

UserDefinedTableAggregateFunction

public interface UserDefinedAggregateFunction
extends UserDefinedFunction

Interface for User Defined Aggregate Functions. E.g. sum, max, count

Method Summary

Modifier and Type	Method	Description
Value	add(Value aggregateKey, Value aggregatedValue, Value toBeAdded)	Handles adding a new value to the current aggregated value.
Value	empty()	The empty/initial aggregate value of this function.
default java.util.Optional<FinalStep>	finalStep()	An optional final step that calculates and returns the result.
default void	init(Value[] args)	This method can be overridden by users to perform initialization logic.
Value	merge(Value aggregateKey, Value first, Value second)	Merges to aggregated values in case of windowing.
DataType	typer(DataType argType)	Defines a mapping from input to output types.

Methods inherited from interface io.lenses.sql.udf.UserDefinedFunction

name, owner, version

Method Detail

typer

DataType typer(DataType argType)
        throws UdfException

Defines a mapping from input to output types.

Parameters:

argType - The data type of the single argument.

Returns:

The data type of the result.

Throws:

UdfException - if the given data type is not supported by this UDF.

empty

Value empty()

The empty/initial aggregate value of this function.

Returns:

the initial value.

init

default void init(Value[] args)

This method can be overridden by users to perform initialization logic. It is guaranteed to be called before empty, add, merge, and in case of table-based aggregations, subtract.

Parameters:

args - The tail of the arguments passed to the UDAF.

add

Value add(Value aggregateKey,
          Value aggregatedValue,
          Value toBeAdded)
   throws UdfException

Handles adding a new value to the current aggregated value.

Parameters:

aggregateKey - The key of the field being aggregated on.

aggregatedValue - The current aggregated value.

toBeAdded - The value to be added to the current aggregated value.

Returns:

The updated aggregated value.

Throws:

UdfException - if adding the new value to the current aggregated value fails.

merge

Value merge(Value aggregateKey,
            Value first,
            Value second)
     throws UdfException

Merges to aggregated values in case of windowing.

Parameters:

aggregateKey - The key of the field being aggregated on.

first - The first aggregated value.

second - The second aggregated value.

Returns:

The combined aggregated value.

Throws:

UdfException - if the merge fails.

finalStep

default java.util.Optional<FinalStep> finalStep()

An optional final step that calculates and returns the result.

Returns:

An optional function that will be called with the aggregated value to calculate the final result.