大数据Spark “蘑菇云”行动第93课：Hive中的内置函数、UDF、UDAF实战
select sum_all(age) from ...
hive> use default;
show tables;
select * from employeeforhaving;
一：udf 编码
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;
public final class LowerCase extends UDF {
  public Text evaluate(final Text s) {
    if (s == null) { return null; }
    return new Text(s.toString().toLowerCase());
  }
}
二：导出jar包  hadoopapps.jar
三，加载jar包
hive> add jar /root/..../hadoopapps.jar
四，hive> CREATE TEMPORARY FUNCTION tolower AS com.dt.spark.hive.HIVEUDF 
五，使用
hive> SELECT tolower(name) from employeeforhaving;
一：UDAF 聚合 编码
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;
  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);
  }
 }
}