org.apache.calcite.adapter.enumerable

Interface AggImplementor

All Known Subinterfaces:

WinAggImplementor

All Known Implementing Classes:

RexImpTable.LagImplementor, RexImpTable.LeadImplementor, RexImpTable.UserDefinedAggReflectiveImplementor, StrictAggImplementor, StrictWinAggImplementor

public interface AggImplementor

Implements an aggregate function by generating expressions to initialize, add to, and get a result from, an accumulator.

See Also:

StrictAggImplementor, StrictWinAggImplementor, RexImpTable.CountImplementor, RexImpTable.SumImplementor

Method Summary

Methods

Modifier and Type	Method and Description
List<Type>	getStateType(AggContext info) Returns the types of the intermediate variables used by the aggregate implementation.
void	implementAdd(AggContext info, AggAddContext add) Updates intermediate values to account for the newly added value.
void	implementReset(AggContext info, AggResetContext reset) Implements reset of the intermediate variables to the initial state.
Expression	implementResult(AggContext info, AggResultContext result) Calculates the resulting value based on the intermediate variables.

Method Detail

getStateType

List<Type> getStateType(AggContext info)

Returns the types of the intermediate variables used by the aggregate implementation.

For instance, for "concatenate to string" this can be StringBuilder. Calcite calls this method before all other implement* methods.

Parameters:

info - Aggregate context

Returns:

Types of the intermediate variables used by the aggregate implementation

implementReset

void implementReset(AggContext info,
                  AggResetContext reset)

Implements reset of the intermediate variables to the initial state. AggResetContext.accumulator() should be used to reference the state variables. For instance, to zero the count, use the following code:

reset.currentBlock().add(
Expressions.statement(
Expressions.assign(reset.accumulator().get(0),
Expressions.constant(0)));

Parameters:

info - Aggregate context

reset - Reset context

implementAdd

void implementAdd(AggContext info,
                AggAddContext add)

Updates intermediate values to account for the newly added value. AggResetContext.accumulator() should be used to reference the state variables.

Parameters:

info - Aggregate context

add - Add context

implementResult

Expression implementResult(AggContext info,
                         AggResultContext result)

Calculates the resulting value based on the intermediate variables. Note: this method must NOT destroy the intermediate variables as calcite might reuse the state when calculating sliding aggregates. AggResetContext.accumulator() should be used to reference the state variables.

Parameters:

info - Aggregate context

result - Result context

Returns:

Expression that is a result of calculating final value of the aggregate being implemented