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From "Emil Ibrishimov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-591) create new type of join ( 1 row for a given key from multiple tables)
Date Tue, 08 Sep 2009 22:51:57 GMT

    [ https://issues.apache.org/jira/browse/HIVE-591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12752808#action_12752808

Emil Ibrishimov commented on HIVE-591:

To support the Hive1 syntax, we will add a PRESERVE keyword to specify which tables to preserve.
For example, to preserve tables A and C:
FROM UNIQUEJOIN A(a.c1,a.c2) PRESERVE, B(b.c1,b.c2), C(c.c1,c.c2) PRESERVE...

The sources of UNIQUEJOINs can only be tables (no subquery support for now)

> create new type of join ( 1 row for a given key from multiple tables)
> ---------------------------------------------------------------------
>                 Key: HIVE-591
>                 URL: https://issues.apache.org/jira/browse/HIVE-591
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Emil Ibrishimov
>         Attachments: HIVE-591.1.patch
> It will be useful to support a new type of join:
> say:
> select .. from JOIN TABLES (A,B,C) WITH KEYS (A.key, B.key, C.key) where ....
> The semantics are that for a given key only 1 row is created - nulls are present for
the the tables which do not contain a row for that key.
> There is no limit on the number of tables, the number of keys should be the same as the
number of tables.

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