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https://issues.apache.org/jira/browse/PIG-1065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12774153#action_12774153
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Santhosh Srinivasan commented on PIG-1065:
------------------------------------------

Answer to Question 1: Pig 1.0 had that syntax and it was retained for backward 
compatibility. Paolo suggested that for uniformity, the 'AS' clause for the 
load statements should be extended to all relational operators. Gradually, the 
column aliasing in the foreach should be removed from the documentation and 
eventually removed from the language.

> 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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