Package 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, FunctionDefinition

Direct Known Subclasses:

AvgAggFunction, Count1AggFunction, CountAggFunction, CumeDistAggFunction, LeadLagAggFunction, ListAggFunction, MaxAggFunction, MinAggFunction, NTILEAggFunction, RankLikeAggFunctionBase, RowNumberAggFunction, SingleValueAggFunction, Sum0AggFunction, SumAggFunction, SumWithRetractAggFunction

@PublicEvolving
public abstract class DeclarativeAggregateFunction
extends 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	Description
DeclarativeAggregateFunction()

Method Summary

Modifier and Type	Method	Description
abstract Expression[]	accumulateExpressions()	Expressions for accumulating the mutable aggregation buffer based on an input row.
abstract UnresolvedReferenceExpression[]	aggBufferAttributes()	All fields of the aggregate buffer.
abstract DataType[]	getAggBufferTypes()	All types of the aggregate buffer.
FunctionKind	getKind()	Returns the kind of function this definition describes.
abstract DataType	getResultType()	The result type of the function.
TypeInference	getTypeInference(DataTypeFactory factory)	Returns the logic for performing type inference of a call to this function definition.
abstract Expression	getValueExpression()	An expression which returns the final value for this aggregate function.
abstract Expression[]	initialValuesExpressions()	Expressions for initializing empty aggregation buffers.
abstract 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 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, supportsConstantFolding

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 DataType[] getAggBufferTypes()

All types of the aggregate buffer.

getResultType

public abstract DataType getResultType()

The result type of the function.

initialValuesExpressions

public abstract Expression[] initialValuesExpressions()

Expressions for initializing empty aggregation buffers.

accumulateExpressions

public abstract Expression[] accumulateExpressions()

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

retractExpressions

public abstract Expression[] retractExpressions()

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

mergeExpressions

public abstract 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 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 FunctionKind getKind()

Description copied from interface: FunctionDefinition

Returns the kind of function this definition describes.

getTypeInference

public TypeInference getTypeInference(DataTypeFactory factory)

Description copied from class: UserDefinedFunction

Returns the logic for performing type inference of a call to this function definition.

The type inference process is responsible for inferring unknown types of input arguments, validating input arguments, and producing result types. The type inference process happens independent of a function body. The output of the type inference is used to search for a corresponding runtime implementation.

Instances of type inference can be created by using TypeInference.newBuilder().

See BuiltInFunctionDefinitions for concrete usage examples.

The type inference for user-defined functions is automatically extracted using reflection. It does this by analyzing implementation methods such as eval() or accumulate() and the generic parameters of a function class if present. If the reflective information is not sufficient, it can be supported and enriched with DataTypeHint and FunctionHint annotations.

Note: Overriding this method is only recommended for advanced users. If a custom type inference is specified, it is the responsibility of the implementer to make sure that the output of the type inference process matches with the implementation method:

The implementation method must comply with each DataType.getConversionClass() returned by the type inference. For example, if DataTypes.TIMESTAMP(3).bridgedTo(java.sql.Timestamp.class) is an expected argument type, the method must accept a call eval(java.sql.Timestamp).

Regular Java calling semantics (including type widening and autoboxing) are applied when calling an implementation method which means that the signature can be eval(java.lang.Object).

The runtime will take care of converting the data to the data format specified by the DataType.getConversionClass() coming from the type inference logic.

Specified by:

getTypeInference in interface FunctionDefinition

Specified by:

getTypeInference in class UserDefinedFunction