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https://issues.apache.org/jira/browse/PIG-1065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12775975#action_12775975
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Dmitriy V. Ryaboy commented on PIG-1065:
----------------------------------------

Aliasing inside foreach is hugely useful for readability. Are you suggesting 
removing the ability to assign aliases inside a forearch, or just to 
change/assign schemas?

> In-determinate behaviour of Union when there are 2 non-matching schema's
> ------------------------------------------------------------------------
>
>                 Key: PIG-1065
>                 URL: https://issues.apache.org/jira/browse/PIG-1065
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.6.0
>            Reporter: Viraj Bhat
>             Fix For: 0.6.0
>
>
> I have a script which first does a union of these schemas and then does a 
> ORDER BY of this result.
> {code}
> f1 = LOAD '1.txt' as (key:chararray, v:chararray);
> f2 = LOAD '2.txt' as (key:chararray);
> u0 = UNION f1, f2;
> describe u0;
> dump u0;
> u1 = ORDER u0 BY $0;
> dump u1;
> {code}
> When I run in Map Reduce mode I get the following result:
> $java -cp pig.jar:$HADOOP_HOME/conf org.apache.pig.Main broken.pig
> ====================
> Schema for u0 unknown.
> ====================
> (1,2)
> (2,3)
> (1)
> (2)
> ====================
> org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1066: Unable to 
> open iterator for alias u1
>         at org.apache.pig.PigServer.openIterator(PigServer.java:475)
>         at 
> org.apache.pig.tools.grunt.GruntParser.processDump(GruntParser.java:532)
>         at 
> org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:190)
>         at 
> org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:166)
>         at 
> org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:142)
>         at org.apache.pig.tools.grunt.Grunt.exec(Grunt.java:89)
>         at org.apache.pig.Main.main(Main.java:397)
> ====================
> Caused by: java.io.IOException: Type mismatch in key from map: expected 
> org.apache.pig.impl.io.NullableBytesWritable, recieved 
> org.apache.pig.impl.io.NullableText
>         at 
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:415)
>         at 
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapReduce$Map.collect(PigMapReduce.java:108)
>         at 
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.runPipeline(PigMapBase.java:251)
>         at 
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapBase.map(PigMapBase.java:240)
>         at 
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapReduce$Map.map(PigMapReduce.java:93)
>         at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:47)
>         at org.apache.hadoop.mapred.MapTask.run(MapTask.java:227)
> ====================
> When I run the same script in local mode I get a different result, as we know 
> that local mode does not use any Hadoop Classes.
> $java -cp pig.jar org.apache.pig.Main -x local broken.pig
> ====================
> Schema for u0 unknown
> ====================
> (1,2)
> (1)
> (2,3)
> (2)
> ====================
> (1,2)
> (1)
> (2,3)
> (2)
> ====================
> Here are some questions
> 1) Why do we allow union if the schemas do not match
> 2) Should we not print an error message/warning so that the user knows that 
> this is not allowed or he can get unexpected results?
> Viraj

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