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Date: Thu, 23 Apr 2009 14:15:30 -0700 (PDT)
From: "Zheng Shao (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Subject: [jira] Updated: (HIVE-164) Support CASE statement using GenericUDF
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     [ https://issues.apache.org/jira/browse/HIVE-164?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zheng Shao updated HIVE-164:
----------------------------

    Attachment: HIVE-164.6.patch

Simplified the interface for GenericUDF. I guess it's easy to write a GenericUDF without too much knowledge of Hive (the developer will still need to know about ObjectInspector).

{code}
@UDFType(deterministic=true)
public abstract class GenericUDF {
  
  /**
   * A Defered Object allows us to do lazy-evaluation
   * and short-circuiting.
   * GenericUDF use DeferedObject to pass arguments.
   */
  public static interface DeferredObject {
    public Object get() throws HiveException; 
  };
  
  /**
   * The constructor
   */
  public GenericUDF() {
  }

  /**
   * Initialize this GenericUDF. This will be called once and only once per
   * GenericUDF instance.
   * 
   * @param arguments     The ObjectInspector for the arguments
   * @throws UDFArgumentTypeException
   *                      Thrown when arguments have wrong types
   * @return              The ObjectInspector for the return value
   */
  public abstract ObjectInspector initialize(ObjectInspector[] arguments) 
      throws UDFArgumentTypeException;
  
  /**
   * Evaluate the GenericUDF with the arguments.
   * @param arguments  The arguments as DeferedObject, use DeferedObject.get() to
   *                   get the actual argument Object.  The Objects can be inspected
   *                   by the ObjectInspectors passed in the initialize call.
   * @return The 
   */
  public abstract Object evaluate(DeferredObject[] arguments) throws HiveException;
  
  /**
   * Get the String to be displayed in explain.
   */
  public abstract String getDisplayString(String[] children);
  
}
{code}


> Support CASE statement using GenericUDF
> ---------------------------------------
>
>                 Key: HIVE-164
>                 URL: https://issues.apache.org/jira/browse/HIVE-164
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Zheng Shao
>            Assignee: Zheng Shao
>         Attachments: HIVE-164.4.patch, HIVE-164.5.patch, HIVE-164.6.patch
>
>
> See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html for details.
> Syntax:
> {code}
> CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [<ELSE result] END
> CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END 
> {code}

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