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https://issues.apache.org/jira/browse/PIG-2715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281277#comment-13281277
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Daniel Dai commented on PIG-2715:
---------------------------------
Yes, alias name for map value is meaningless. We shall clearly document it.
> Cannot specify schema field alias for map value via piglatin
> ------------------------------------------------------------
>
> Key: PIG-2715
> URL: https://issues.apache.org/jira/browse/PIG-2715
> Project: Pig
> Issue Type: Bug
> Components: parser
> Affects Versions: 0.10.0
> Reporter: Andy Schlaikjer
>
> Programmatically, pig components are able to define schema field aliases for
> map values, but the same cannot be done via piglatin. For example:
> {code}
> %default INPUT_PATH 'map_value_alias_bug.tsv';
> A = LOAD '$INPUT_PATH' AS (
> id: long,
> -- events: [count: int] -- parse failure
> events: [int]
> );
> DESCRIBE A;
> A = FOREACH A GENERATE
> id,
> -- (map[count: int]) events -- parse failure
> -- ([count: int]) events -- parse failure
> -- events: [count: int] -- parse failure
> -- events AS [count: int] -- parse failure
> -- events AS events: [count: int] -- parse failure
> ([int]) events -- this is okay
> ;
> DESCRIBE A;
> quit;
> {code}
> When using the [Elephant Bird
> project|https://github.com/kevinweil/elephant-bird/]'s [ThriftToPig
> utility|https://github.com/kevinweil/elephant-bird/blob/master/src/java/com/twitter/elephantbird/pig/util/ThriftToPig.java#L273]
> along with a Thrift message spec containing a map field, I see schemas of
> the following form:
> {code}
> message: {id: long,events: map[events: int])}}
> {code}
> This same DESCRIBE output does not parse if used within piglatin.
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