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https://issues.apache.org/jira/browse/PIG-1014?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764755#action_12764755
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Pradeep Kamath commented on PIG-1014:
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The jira is to track if it is possible to automatically convert a
COUNT(relation) in the script to COUNT_STAR(relation) in the plan so that
nullness of the fields in the records is not considered while returning the
count. For example if a relation (A) has two fields and there is the following
script snippet:
{noformat}
B = group A by $0;
C = foreach B generate group, COUNT(A);
{noformat}
This is equivalent to a count(*) after grouping on the first column in SQL. Per
SQL semantics, COUNT(*) counts all records for the group without regard to the
nullness of the individual fields. This behavior is achieved through COUNT_STAR
built -in in pig. However COUNT built-in in pig is meant for counting a bag
with a single column (for example COUNT(A.$0) above). So the implementation
in COUNT checks if the first field in the bag is null or not and only counts
non null values. In the above script if the first column in the bag is null for
any record, it does not get counted which would not be the same as the expected
result for COUNT(*) in SQL. So if the compilation phase in pig can detect that
the COUNT is being performed on a whole relation (rather than an individual
column), it can replace the COUNT with COUNT_STAR and achieve the desired
result.
> Pig should convert COUNT(relation) to COUNT_STAR(relation) so that all
> records are counted without considering nullness of the fields in the records
> ----------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: PIG-1014
> URL: https://issues.apache.org/jira/browse/PIG-1014
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.4.0
> Reporter: Pradeep Kamath
>
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