org.apache.flink.table.api.functions.TableFunction Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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*/
package org.apache.flink.table.api.functions;
import org.apache.flink.table.api.types.DataType;
import org.apache.flink.util.Collector;
/**
* 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 {@link 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 {@link DataType} of the result type
* can be manually defined by overriding {@link #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.
*
*
Example:
*
* {@code
*
* public class Split extends TableFunction {
*
* // 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 ...
* }
*
* val tEnv: TableEnvironment = ...
* val table: Table = ... // schema: [a: String]
*
* // for Scala users
* val split = new Split()
* table.join(split('c) as ('s)).select('a, 's)
*
* // for Java users
* tEnv.registerFunction("split", new Split()) // register table function first
* table.join(new Table(tEnv, "split(a) as (s)")).select("a, s")
*
* // for SQL users
* tEnv.registerFunction("split", new Split()) // register table function first
* tEnv.sql("SELECT a, s FROM MyTable, LATERAL TABLE(split(a)) as T(s)")
*
* }
*
* @param The type of the output row
*/
public abstract class TableFunction extends CustomTypeDefinedFunction {
/**
* Emit an output row.
*
* @param row the output row
*/
public void collect(T row) {
collector.collect(row);
}
// ----------------------------------------------------------------------------------------------
/**
* The code generated collector used to emit row.
*/
private Collector collector = null;
/**
* Internal use. Sets the current collector.
*/
public final void setCollector(Collector collector) {
this.collector = collector;
}
}