org.apache.flink.table.functions

Class TableFunction<T>

java.lang.Object

org.apache.flink.table.functions.UserDefinedFunction

org.apache.flink.table.functions.TableFunction<T>

Type Parameters:

T - The type of the output row

All Implemented Interfaces:

Serializable, FunctionDefinition

Direct Known Subclasses:

TemporalTableFunction

@PublicEvolving
public abstract class TableFunction<T>
extends UserDefinedFunction

Base class for a user-defined table function (UDTF). A user-defined table functions works on zero, one, or multiple scalar values as input and returns multiple rows as output.

The behavior of a TableFunction can be defined by implementing a custom evaluation method. An evaluation method must be declared publicly, not static, 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().

Internally, the Table/SQL API code generation works with primitive values as much as possible. If a user-defined table 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.

For Example:

 
   public class Split extends TableFunction<String> {

     // implement an "eval" method with as many parameters as you want
     public void eval(String str) {
       for (String s : str.split(" ")) {
         collect(s);   // use collect(...) to emit an output row
       }
     }

     // you can overload the eval method here ...
   }

   TableEnvironment tEnv = ...
   Table table = ...    // schema: ROW(a VARCHAR)

   // for Scala users
   val split = new Split()
   table.joinLateral(split('a) as ('s)).select('a, 's)

   // for Java users
   tEnv.registerFunction("split", new Split());   // register table function first
   table.joinLateral("split(a) as (s)").select("a, s");

   // for SQL users
   tEnv.registerFunction("split", new Split());   // register table function first
   tEnv.sqlQuery("SELECT a, s FROM MyTable, LATERAL TABLE(split(a)) as T(s)");
 
 

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected org.apache.flink.util.Collector<T>	collector The code generated collector used to emit rows.

Constructor Summary

Constructors

Constructor and Description
TableFunction()

Method Summary

Modifier and Type	Method and Description
protected void	collect(T row) Emits an output row.
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<T>	getResultType() Returns the result type of the evaluation method with a given signature.
void	setCollector(org.apache.flink.util.Collector<T> collector) Internal use.

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

Field Detail

collector

protected org.apache.flink.util.Collector<T> collector

The code generated collector used to emit rows.

Constructor Detail

TableFunction

public TableFunction()

Method Detail

setCollector

public final void setCollector(org.apache.flink.util.Collector<T> collector)

Internal use. Sets the current collector.

getResultType

public org.apache.flink.api.common.typeinfo.TypeInformation<T> getResultType()

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.

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

collect

protected final void collect(T row)

Emits an output row.

Parameters:

row - the output row

getKind

public final FunctionKind getKind()

Description copied from interface: FunctionDefinition

Returns the kind of function this definition describes.