flink-自定义聚合函数

定义

自定义聚合函数（UDAF），将多条记录聚合成1条记录。其输入与输出是多对一的关系，即将多条输入记录聚合成一条输出值。

详情可查看：https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/functions/udfs/#aggregate-functions

函数注册

增加依赖：

<dependencies>

　　 <dependency>

　　　　 <groupId>org.apache.flink</groupId>

　　　　<artifactId>flink-table-common</artifactId>

　　　　<version>1.12.7</version>

　　　　 <scope>provided</scope>

　　</dependency>

</dependencies>

代码示例：　　

package com.flink;

import org.apache.flink.table.functions.AggregateFunction;

import java.util.Iterator;

public class ASI_UDAF {
public static class AccSum {
public long sum;
}

public static class MySum extends AggregateFunction<Long, AccSum> {

@Override
public Long getValue(AccSum acSum) {
return acSum.sum;
}

@Override
public AccSum createAccumulator() {
AccSum acCount = new AccSum();
acCount.sum = 0;
return acCount;
}

public void accumulate(AccSum acc, long num) {
acc.sum += num;
}

/**
* Support retract a msg generated by upstream operator.
*/
public void retract(AccSum acc, long num) {
acc.sum -= num;
}

/**
* Support local-global two stage aggregate optimization.
*/
public void merge(AccSum acc, Iterable<AccSum> it) {
Iterator<AccSum> iter = it.iterator();
while (iter.hasNext()) {
AccSum accSum = iter.next();
if (null != accSum) {
acc.sum += accSum.sum;
}
}
}
}
}

函数应用示例

CREATE TEMPORARY TABLE ASI_UDAF_Source (

  a BIGINT NOT NULL

) WITH (

  'connector' = 'datagen'

);

CREATE TEMPORARY TABLE ASI_UDAF_Sink (

  a  BIGINT

) WITH (

  'connector' = 'print'

);

INSERT INTO ASI_UDAF_Sink

SELECT `ASI_UDAF$MySum`(a) FROM ASI_UDAF_Source;