HIVE自动生成索引

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目前HIVE当中并没有相应的api用于自动生成相应的索引，在一般的sql中包含了identity函数可以用于自动生成相应的索引，为了解决这个问题，在apache官网上提供了相应的解决方法，这个功能还是比较实用的，比如博主需要处理的字段数据中一部分是全部数字，但是有些数据是字符和数字的组合，需要对这些数据做相同的函数处理有的时候是无法做到的，因此可以将其映射到一个额外的字段，到时处理的结果返回再次映射回到最初的数据。

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package org.apache.hadoop.hive.contrib.udf;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.udf.UDFType;
import org.apache.hadoop.io.LongWritable;

/**
 * UDFRowSequence.
 */
@Description(name = "row_sequence",
    value = "_FUNC_() - Returns a generated row sequence number starting from 1")
@UDFType(deterministic = false, stateful = true)
public class UDFRowSequence extends UDF
{
  private LongWritable result = new LongWritable();

  public UDFRowSequence() {
    result.set(0);
  }

  public LongWritable evaluate() {
    result.set(result.get() + 1);
    return result;
  }
}

// End UDFRowSequence.java

可以将其打包成jar包，然后再hive查询中导入作为UDF，这样就可以实现字段的自动索引