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From "Aniket Mokashi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-972) Make describe work with nested foreach
Date Thu, 03 Jun 2010 18:52:58 GMT

    [ https://issues.apache.org/jira/browse/PIG-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875242#action_12875242
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Aniket Mokashi commented on PIG-972:
------------------------------------

Approach-
1. To implement above mentioned functionality, parser keeps track of all the nested aliases
it comes across and adds them to LOForEach.
2. After we parse the query (foreach), we dump the schema for all nested-aliases stored in
the list.
3. When describe foreach-alias; is queried, along with schema for foreach-alias, we dump the
schema for all nested-aliases stored in the list.

Data Structures -
Adding mDescribedAliasList to LOForEach to list all the "described" nested aliases.
LOForeach has mForEachPlans which creates plan for all projections. This keeps track of schemas
for all nested aliases inside leaves of its plans.

Issues-
Verification of aliases in nested describe- As, we do not create a map for nested aliases,
it is not possible to validate upfront the name of the alias used in nested describe.
Multiple dumps- Above approach might lead to multiple dumping of schemas.
These issues can be solved with adding more state into LOForeach. 


> Make describe work with nested foreach
> --------------------------------------
>
>                 Key: PIG-972
>                 URL: https://issues.apache.org/jira/browse/PIG-972
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Olga Natkovich
>            Assignee: Aniket Mokashi
>             Fix For: 0.8.0
>
>
> Currently Parser can't deal with that. This is because describe is part of Grunt parser
while the rest of nested foreach is handled by the QueryParser

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