org.apache.flink.table.functions

Class DeclarativeAggregateFunction

java.lang.Object

org.apache.flink.table.functions.UserDefinedFunction

org.apache.flink.table.functions.DeclarativeAggregateFunction

All Implemented Interfaces:

Serializable, org.apache.flink.table.functions.FunctionDefinition

@PublicEvolving
public abstract class DeclarativeAggregateFunction
extends org.apache.flink.table.functions.UserDefinedFunction

API for aggregation functions that are expressed in terms of expressions.

When implementing a new expression-based aggregate function, you should first decide how many operands your function will have by implementing operandCount() method. And then you can use operand(int) fields to represent your operand, like `operand(0)`, `operand(2)`.

Then you should declare all your buffer attributes by implementing aggBufferAttributes(). You should declare all buffer attributes as UnresolvedReferenceExpression, and make sure the name of your attributes are unique within the function and it should not conflict with operandIndex. You can then use these attributes when defining initialValuesExpressions(), accumulateExpressions(), mergeExpressions() and getValueExpression().

Note: Developer of DeclarativeAggregateFunction should guarantee that the inferred type of getValueExpression() is the same as getResultType()

See an full example: AvgAggFunction.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
DeclarativeAggregateFunction()

Method Summary

Modifier and Type	Method and Description
abstract org.apache.flink.table.expressions.Expression[]	accumulateExpressions() Expressions for accumulating the mutable aggregation buffer based on an input row.
abstract UnresolvedReferenceExpression[]	aggBufferAttributes() All fields of the aggregate buffer.
abstract org.apache.flink.table.types.DataType[]	getAggBufferTypes() All types of the aggregate buffer.
org.apache.flink.table.functions.FunctionKind	getKind()
abstract org.apache.flink.table.types.DataType	getResultType() The result type of the function.
org.apache.flink.table.types.inference.TypeInference	getTypeInference(org.apache.flink.table.catalog.DataTypeFactory factory)
abstract org.apache.flink.table.expressions.Expression	getValueExpression() An expression which returns the final value for this aggregate function.
abstract org.apache.flink.table.expressions.Expression[]	initialValuesExpressions() Expressions for initializing empty aggregation buffers.
abstract org.apache.flink.table.expressions.Expression[]	mergeExpressions() A sequence of expressions for merging two aggregation buffers together.
UnresolvedReferenceExpression	mergeOperand(UnresolvedReferenceExpression aggBuffer) Merge input of mergeExpressions(), the input are AGG buffer generated by user definition.
UnresolvedReferenceExpression[]	mergeOperands() Merge inputs of mergeExpressions(), these inputs are agg buffer generated by user definition.
UnresolvedReferenceExpression	operand(int i) Arg of accumulate and retract, the input value (usually obtained from a new arrived data).
abstract int	operandCount() How many operands your function will deal with.
UnresolvedReferenceExpression[]	operands() Args of accumulate and retract, the input value (usually obtained from a new arrived data).
abstract org.apache.flink.table.expressions.Expression[]	retractExpressions() Expressions for retracting the mutable aggregation buffer based on an input row.

Methods inherited from class org.apache.flink.table.functions.UserDefinedFunction

close, functionIdentifier, open, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.flink.table.functions.FunctionDefinition

getRequirements, isDeterministic

Constructor Detail

DeclarativeAggregateFunction

public DeclarativeAggregateFunction()

Method Detail

operandCount

public abstract int operandCount()

How many operands your function will deal with.

aggBufferAttributes

public abstract UnresolvedReferenceExpression[] aggBufferAttributes()

All fields of the aggregate buffer.

getAggBufferTypes

public abstract org.apache.flink.table.types.DataType[] getAggBufferTypes()

All types of the aggregate buffer.

getResultType

public abstract org.apache.flink.table.types.DataType getResultType()

The result type of the function.

initialValuesExpressions

public abstract org.apache.flink.table.expressions.Expression[] initialValuesExpressions()

Expressions for initializing empty aggregation buffers.

accumulateExpressions

public abstract org.apache.flink.table.expressions.Expression[] accumulateExpressions()

Expressions for accumulating the mutable aggregation buffer based on an input row.

retractExpressions

public abstract org.apache.flink.table.expressions.Expression[] retractExpressions()

Expressions for retracting the mutable aggregation buffer based on an input row.

mergeExpressions

public abstract org.apache.flink.table.expressions.Expression[] mergeExpressions()

A sequence of expressions for merging two aggregation buffers together. When defining these expressions, you can use the syntax attributeName and mergeOperand(attributeName) to refer to the attributes corresponding to each of the buffers being merged.

getValueExpression

public abstract org.apache.flink.table.expressions.Expression getValueExpression()

An expression which returns the final value for this aggregate function.

operands

public final UnresolvedReferenceExpression[] operands()

Args of accumulate and retract, the input value (usually obtained from a new arrived data).

operand

public final UnresolvedReferenceExpression operand(int i)

Arg of accumulate and retract, the input value (usually obtained from a new arrived data).

mergeOperand

public final UnresolvedReferenceExpression mergeOperand(UnresolvedReferenceExpression aggBuffer)

Merge input of mergeExpressions(), the input are AGG buffer generated by user definition.

mergeOperands

public final UnresolvedReferenceExpression[] mergeOperands()

Merge inputs of mergeExpressions(), these inputs are agg buffer generated by user definition.

getKind

public org.apache.flink.table.functions.FunctionKind getKind()

getTypeInference

public org.apache.flink.table.types.inference.TypeInference getTypeInference(org.apache.flink.table.catalog.DataTypeFactory factory)

Specified by:

getTypeInference in interface org.apache.flink.table.functions.FunctionDefinition

Specified by:

getTypeInference in class org.apache.flink.table.functions.UserDefinedFunction