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Hive, mail # user - Calling same UDF multiple times in a SELECT query


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Re: Calling same UDF multiple times in a SELECT query
Jan Dolinár 2013-07-23, 19:35
Hi,

If you use annotation, Hive should be able to optimize it to single call:

 @UDFType(deterministic = true)

The obvious condition is that it must always return the identical result
when called with same parameters.

Little bit more on this can be found in Mark Grovers post at
http://mark.thegrovers.ca/1/post/2012/06/how-to-write-a-hive-udf.html.

Regards,
Jan
On Tue, Jul 23, 2013 at 9:25 PM, Nitin Pawar <[EMAIL PROTECTED]>wrote:

> fucntion return values are not stored for repeat use of same (as per my
> understanding)
>
> I know you may have already thought about other approach as
>
> select a , if (call <-1, -1 call) as b from (select a, fooudf(a) as call
> from table
>
>
>
>
> On Wed, Jul 24, 2013 at 12:42 AM, Sanjay Subramanian <
> [EMAIL PROTECTED]> wrote:
>
>>  Hi
>>
>>  V r using version hive-exec-0.9.0-cdh4.1.2 in production
>>
>>  I need to check and use the output from a UDF in a query to assign
>> values to 2 columns in a SELECT query
>>
>>  Example
>>
>>  SELECT
>>      a,
>>      IF(fooUdf(a) < -1  , -1, fooUdf(a)) as b,
>>      IF(fooUdf(a) < -1  , fooUdf(a), 0) as c
>> FROM
>>      my_hive_table
>>
>>
>>  So will fooUdf be called 4 times ? Or once ?
>>
>>  Why this is important is because in our case this UDF calls a web
>> service and I don't want so many calls to the service.
>>
>>  Thanks
>>
>>  sanjay
>>
>>
>>
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>
>
>
> --
> Nitin Pawar
>