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https://issues.apache.org/jira/browse/PIG-1036?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12772157#action_12772157
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Pradeep Kamath commented on PIG-1036:
-------------------------------------

In the unit tests in TestFRJoin, there is a check made for the output tuples 
using hasmaps and also using TestHelper.compareBags() - are both required?

In QueryParser.jjt we currently have:
{code}
1974         // in the case of outer joins, only two
| 1975         // inputs are allowed
| 1976         isOuter = (isLeftOuter || isRightOuter || isFullOuter);
| 1977         if(isOuter && gis.size() > 2) {
| 1978           throw new ParseException("(left|right|full) outer joins are 
only supported for two inputs");
| 1979         }
{code}
        
I think left outer join should only be supported for 2 way FR joins - looks 
like the code supports >=2 inputs - 
{code}
 867                 // This condition may not reach, as a join has more than 
one side
   868                 if( innerFlags.length >= 2 ) {
   869                     isLeftOuter = !innerFlags[1];
   870                 }
{code}

In the code below, TupleFactory.getInstance() can be replaced with 
mTupleFactory. Also there should be checks to see if the second input
has a schema and we should rely on that to determine how many nulls are needed. 
Left outer join should only be supported for the case
where second input has a schema (assuming we only support 2 way FR join) to be 
consistent in all our implementations of left join. 
209                         Tuple nullTuple = 
TupleFactory.getInstance().newTuple(iter.next().get(0).size());   

Why is an array of Bags (nullBags) used? should this be nullTuples since what 
we really want is just 1 null tuple - also if we only
support 2 way left outer join, this would just be a nullTuple instead of an 
array.



> Fragment-replicate left outer join
> ----------------------------------
>
>                 Key: PIG-1036
>                 URL: https://issues.apache.org/jira/browse/PIG-1036
>             Project: Pig
>          Issue Type: New Feature
>            Reporter: Olga Natkovich
>            Assignee: Ankit Modi
>         Attachments: LeftOuterFRJoin.patch
>
>


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