[jira] Commented: (HIVE-591) create new type of join ( 1 row for a given key from multiple tables)

["Raghotham Murthy (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12725357#action_12725357 ] 

Raghotham Murthy commented on HIVE-591:
---------------------------------------

It might be better to associate the keys with the tables explicitly instead of implicitly via ordering. How about something like:

SELECT ... FROM UNIQUEJOIN A(expr_with_A_cols), B(expr_with_B_cols), C(expr_with_C_cols) WHERE ...

expr_with_<TAB>_cols will be the join key for the corresponding <TAB>

> 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
>
> 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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