Package dev.frostlake.functions.aggregate

Class ApproxPercentileAccumulator

java.lang.Object

dev.frostlake.functions.aggregate.ApproxPercentileAccumulator

All Implemented Interfaces:

AggregateFunction.Accumulator

public class ApproxPercentileAccumulator
extends Object
implements AggregateFunction.Accumulator

Accumulator for APPROX_PERCENTILE(expr, percentile). Snowflake computes an approximate percentile from a t-digest sketch; this emulator computes the exact interpolated percentile (identical to PERCENTILE_CONT), which is the best possible approximation and matches Snowflake within its documented error bound for typical data. The percentile (a constant in [0, 1]) is supplied by the executor from the function's second argument via setPercentile(double).

Constructor Summary

Constructors

Constructor	Description
ApproxPercentileAccumulator()

Method Summary

Modifier and Type	Method	Description
void	accumulate(Object value)	Folds one row's argument value into the running state.
Object	getResult()	The aggregate's result over everything accumulated so far.
void	merge(AggregateFunction.Accumulator other)	Folds another accumulator's state into this one, combining two partial aggregations of the same group.
void	reset()	Clears the state back to the empty-group starting point so the accumulator can be reused.
void	setPercentile(double percentile)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ApproxPercentileAccumulator

public ApproxPercentileAccumulator()

Method Details

setPercentile

public void setPercentile(double percentile)

accumulate

public void accumulate(Object value)

Description copied from interface: AggregateFunction.Accumulator

Folds one row's argument value into the running state.

Specified by:

accumulate in interface AggregateFunction.Accumulator

Parameters:

value - the aggregate argument's value for one row; SQL NULL arrives as null

getResult

public Object getResult()

Description copied from interface: AggregateFunction.Accumulator

The aggregate's result over everything accumulated so far.

Specified by:

getResult in interface AggregateFunction.Accumulator

Returns:

the group's result, or null where the aggregate defines an empty group as NULL

reset

public void reset()

Description copied from interface: AggregateFunction.Accumulator

Clears the state back to the empty-group starting point so the accumulator can be reused.

Specified by:

reset in interface AggregateFunction.Accumulator

merge

public void merge(AggregateFunction.Accumulator other)

Description copied from interface: AggregateFunction.Accumulator

Folds another accumulator's state into this one, combining two partial aggregations of the same group.

Specified by:

merge in interface AggregateFunction.Accumulator

Parameters:

other - a partial state of the same aggregate implementation