Add some UDFs which help to migrate Oracle to Hive
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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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