package com.udf;

import org.apache.hadoop.hive.ql.exec.UDF;

import org.apache.hadoop.io.Text;

public class RowNumUDF extends UDF{

	public static String signature = "_";

	public static int order = 0;

	public int evaluate(Text text){

		if(text != null){

			//分组排序的依据，列名，通常为主键

			String colName = text.toString();

			//处理第一条数据

			if(signature == "_"){

				//记下分组排序的字段：主键，并将rownum设为1

				signature = colName;

				order = 1;

				//返回rownum

				return order;

			}else{

			//首先比对是否和上一条主键相同

			if(signature.equals(colName)){

				//rownum依次加1

				order++;

				return order;

			}else{

					//如果主键改变，将rownum设为1

					signature = colName;

					order = 1;

					return order;

				}

			}

		}else{

			//如果主键为空，则返回-1

			return -1;

		}

	}

}