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From "JunHo Cho (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-2361) Add some UDFs which help to migrate Oracle to Hive
Date Tue, 09 Aug 2011 01:26:29 GMT
 Add some UDFs which help to migrate Oracle to Hive
---------------------------------------------------

                 Key: HIVE-2361
                 URL: https://issues.apache.org/jira/browse/HIVE-2361
             Project: Hive
          Issue Type: New Feature
          Components: UDF
    Affects Versions: 0.8.0
            Reporter: JunHo Cho
            Priority: Minor
         Attachments: nexr-udf.tar

Here some UDFs which can be matched to oracle functions:
There are two kinds of oracle functions. one is scalar function and another is analytic function.
Most scalar functions in Oracle can be converted to hive's udf directly.  

Oracle Scalar Function

GenericUDFDecode : Compares first argument to each other value one by one. e.g., DECODE(x,0,'zero',1,'one')
will return 'zero' if x is 0
GenericUDFGreatest : Return the greatest of the list of one or more expressions. e.g., GREATEST(2,5,12,3)
will return 12
GenericUDFInstr : Return the location of a substring in a string. e.g., INSTR('next', 'e')
will return 2
GenericUDFLnnvl : Evaluate a condition when one or both operands of the condition may be null.
e.g., LNNVL(2 > 4) will return true
GenericUDFNVL : Replace null with a string in the results of a query. e.g., NVL(null,'hive')
will return hive
GenericUDFNVL2 : Determine the value returned by a query based on whether a specified expression
is null or not null. e.g., NVL2(null,'not null','null value') will return 'null value'
GenericUDFToNumber : Convert a string to a number. e.g., TO_NUMBER('112','999') will return
112
GenericUDFTrunc : Returns a date truncated to a specific unit of measure. e.g., TRUNC('2002-11-02
01:01:01','YYYY') will return '2002-01-01 00:00:00'


Oracle Analytic Function

Most analytic functions in Oracle can't be converted to hive's query and udf directly.
Following udfs should be used with DISTRIBUTED, SORT BY and HASH of hive to support analytic
functions 

e.q., SELECT _FUNC_(hash(col1), col2, ...) FROM SELECT ~ FROM table DISTRIBUTED BY hash(col1)
SORT BY col1, col2 ...

GenericUDFSum : Calculate a cumulative sum.
GenericUDFRank : Assign a sequential order, or rank within some group based on key.
GenericUDFDenseRank : Act like RANK function except that it assigns consecutive ranks.
GenericUDFRowNumber : Return sequence integer value within some group based on key.
GenericUDFMax : Determine the highest value within some group based on key.
GenericUDFMin : Determine the lowest value within some group based on key.
GenericUDFLag : Access data from a previous row.

This udfs was developed with hive-pdk


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