目標實現

1a

1b

2a

2c

轉換為

1a,b

2a,c

package com.hive.udf;

//用法 select a,concat1(b,',') from concat_test group by a;
import org.apache.hadoop.hive.ql.exec.UDAF;
import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;
public class Concat extends UDAF {
 public static class ConcatUDAFEvaluator implements UDAFEvaluator{
  public static class PartialResult{
   String result;
   String delimiter;
  }
  private PartialResult partial;
  //init函式實現介面UDAFEvaluator的init函式。
  public void init() {
   partial = null;
  }
  //iterate接收傳入的引數，並進行內部的輪轉。其返回型別為boolean。
  //接受傳入的引數，並進行內部的輪轉
  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;
  }
  //terminatePartial無引數，其為iterate函式輪轉結束後，返回輪轉資料，terminatePartial類似於hadoop的Combiner。
  
  public PartialResult terminatePartial(){
   return partial;
  }
  
  //merge接收terminatePartial的返回結果，進行資料merge操作，其返回型別為boolean。
  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);
  }
 }
}
 

add jar rowtocol.jar

create temporary function concat_test as'com.hive.udf.Concat'; 

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