CODEWITHSUNDEEP
sqlhivepartitionwindowing
Prashasti
Prashasti

Reputation: 115

How to select last NON-NULL values of each column in a Hive partition

I have a hive-table containing transactional data of the form (highly simplified)

id  Status  Value   UpdatedTimeStamp

515 Open    1   2014-05-08T11:43:27
516 Open    NULL    2014-05-08T11:43:27
515 Answered    1   2014-05-09T11:43:27 
515 Closed  NULL    2014-05-10T11:43:27
517 Open    NULL    2014-05-09T11:43:27
516 Closed  NULL    2014-05-09T11:43:27

For my use-case, I need an output table containing unique ids with column entries as the last non-NULL value in that column for that particular id when sorted by timestamp.

Hence, the desired output is:

id  Status  Value   UpdatedTimeStamp

515 Closed  1   2014-05-10T11:43:27
516 Closed  NULL    2014-05-09T11:43:27
517 Open    NULL    2014-05-09T11:43:27

I am trying to achieve that by using windowing functions on partitions

INSERT OVERWRITE TABLE testSample2 SELECT id, FIRST_VALUE (Status) OVER SortedData, FIRST_VALUE (Value IGNORE NULLS) OVER SortedData, FIRST_VALUE (UpdatedTimeStamp) OVER SortedData FROM testSample WINDOW SortedData (PARTITION BY id ORDER BY UpdatedTimeStamp DESC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING);

This gives me NullPointerException (Probably, IGNORE NULLS is not yet supported in Hive). Please suggest me how to take the last non-NULL value.

Upvotes: 2

Views: 2080

Answers (1)

Kirill Sultanov
Kirill Sultanov

Reputation: 11

Try to use something like this:

select ss.vl1, FIRST_VALUE(ss.ky) OVER (PARTITION BY ss.vl1 ORDER BY ss.nl, ss.vl rows unbounded preceding) 
FROM (
    SELECT IF(s.vl=123456, 'sasa', 'AAAAAA') as vl1, s.vl, s.ky, IF(s.ky IS NULL, 1, 0) as nl
    FROM (
        select explode(map(NULL, 123, 1, 1234, 2, 12345, 3, 123456)) as (ky, vl) from default.dual) s ) ss;
vl1     _wcol0
AAAAAA  1
AAAAAA  1
AAAAAA  1
sasa    3

Upvotes: 1

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