hive中自定义函数(UDAF)实现多行字符串拼接为一行，

hive中自定义函数(UDAF)实现多行字符串拼接为一行，

函数如何使用：

hive> desc concat_test;
OK
a       int
b       string

hive> select * from concat_test;
OK
1       good
2       other
1       nice
1       hello

hive> select a,concat(b,',') from concat_test group by a;

OK
1       good,nice,hello
2       other

 

函数实现：

import org.apache.hadoop.hive.ql.exec.UDAF;
import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;

public class ConnectGroup extends UDAF{
	
 public static class ConcatUDAFEvaluator implements UDAFEvaluator{
	 
  public static class PartialResult{
   String result;
   String delimiter;
  }
  
  private PartialResult partial;
  
  public void init() {
	  partial = null;
  }
  
  public boolean iterate(String value, String deli){
   
   if(value == null){
	   return true;
   }
   
   if(partial == null){
	   partial = new PartialResult();
	   partial.result = new String("");
	   if(deli == null || deli.equals("")){
		   partial.delimiter = new String(",");
	   }
	   else{
		   partial.delimiter = new String(deli);
	   }
   }
   if( partial.result.length() > 0 ){
	   partial.result = partial.result.concat(partial.delimiter);
   }
   partial.result = partial.result.concat(value);
   return true;
  }
  
  public PartialResult terminatePartial(){
	  return partial;
  }
  
  public boolean merge(PartialResult other){
   if (other == null){
	   return true;
   }
   if (partial == null){
	    partial = new PartialResult();
	    partial.result = new String(other.result);
	    partial.delimiter = new String(other.delimiter);
   }
   else{
	   if ( partial.result.length() > 0 ){
		   partial.result = partial.result.concat(partial.delimiter);
	   }
	   partial.result = partial.result.concat(other.result);
   }
   return true;
  }
  
  public String terminate(){
	  return new String(partial.result);
  }
 }
}