org.apache.flink.table.functions

Class ScalarFunction

java.lang.Object

org.apache.flink.table.functions.UserDefinedFunction

org.apache.flink.table.functions.ScalarFunction

All Implemented Interfaces:

Serializable, FunctionDefinition

@PublicEvolving
public abstract class ScalarFunction
extends UserDefinedFunction

Base class for a user-defined scalar function. A user-defined scalar functions maps zero, one, or multiple scalar values to a new scalar value.

The behavior of a ScalarFunction can be defined by implementing a custom evaluation method. An evaluation method must be declared publicly and named eval. Evaluation methods can also be overloaded by implementing multiple methods named eval.

User-defined functions must have a default constructor and must be instantiable during runtime.

By default the result type of an evaluation method is determined by Flink's type extraction facilities. This is sufficient for basic types or simple POJOs but might be wrong for more complex, custom, or composite types. In these cases TypeInformation of the result type can be manually defined by overriding getResultType(java.lang.Class<?>[]).

Internally, the Table/SQL API code generation works with primitive values as much as possible. If a user-defined scalar function should not introduce much overhead during runtime, it is recommended to declare parameters and result types as primitive types instead of their boxed classes. DATE/TIME is equal to int, TIMESTAMP is equal to long.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
ScalarFunction()

Method Summary

Modifier and Type	Method and Description
FunctionKind	getKind() Returns the kind of function this definition describes.
org.apache.flink.api.common.typeinfo.TypeInformation<?>[]	getParameterTypes(Class<?>[] signature) Returns TypeInformation about the operands of the evaluation method with a given signature.
org.apache.flink.api.common.typeinfo.TypeInformation<?>	getResultType(Class<?>[] signature) Returns the result type of the evaluation method with a given signature.

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

ScalarFunction

public ScalarFunction()

Method Detail

getResultType

public org.apache.flink.api.common.typeinfo.TypeInformation<?> getResultType(Class<?>[] signature)

Returns the result type of the evaluation method with a given signature.

This method needs to be overridden in case Flink's type extraction facilities are not sufficient to extract the TypeInformation based on the return type of the evaluation method. Flink's type extraction facilities can handle basic types or simple POJOs but might be wrong for more complex, custom, or composite types.

Parameters:

signature - signature of the method the return type needs to be determined

Returns:

TypeInformation of result type or null if Flink should determine the type

getParameterTypes

public org.apache.flink.api.common.typeinfo.TypeInformation<?>[] getParameterTypes(Class<?>[] signature)

Returns TypeInformation about the operands of the evaluation method with a given signature.

In order to perform operand type inference in SQL (especially when NULL is used) it might be necessary to determine the parameter TypeInformation of an evaluation method. By default Flink's type extraction facilities are used for this but might be wrong for more complex, custom, or composite types.

Parameters:

signature - signature of the method the operand types need to be determined

Returns:

TypeInformation of operand types

getKind

public final FunctionKind getKind()

Description copied from interface: FunctionDefinition

Returns the kind of function this definition describes.