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From "Takeshi Yamamuro (Jira)" <j...@apache.org>
Subject [jira] [Updated] (SPARK-27877) ANSI SQL: LATERAL derived table(T491)
Date Sun, 29 Dec 2019 00:22:00 GMT

     [ https://issues.apache.org/jira/browse/SPARK-27877?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Takeshi Yamamuro updated SPARK-27877:
-------------------------------------
    Parent Issue: SPARK-30374  (was: SPARK-27764)

> ANSI SQL: LATERAL derived table(T491)
> -------------------------------------
>
>                 Key: SPARK-27877
>                 URL: https://issues.apache.org/jira/browse/SPARK-27877
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 3.0.0
>            Reporter: Yuming Wang
>            Priority: Major
>
> Subqueries appearing in {{FROM}} can be preceded by the key word {{LATERAL}}. This
allows them to reference columns provided by preceding {{FROM}} items. (Without {{LATERAL}},
each subquery is evaluated independently and so cannot cross-reference any other {{FROM}} item.)
> Table functions appearing in {{FROM}} can also be preceded by the key word {{LATERAL}},
but for functions the key word is optional; the function's arguments can contain references
to columns provided by preceding {{FROM}} items in any case.
> A {{LATERAL}} item can appear at top level in the {{FROM}} list, or within a {{JOIN}} tree.
In the latter case it can also refer to any items that are on the left-hand side of a {{JOIN}} that
it is on the right-hand side of.
> When a {{FROM}} item contains {{LATERAL}} cross-references, evaluation proceeds as
follows: for each row of the {{FROM}} item providing the cross-referenced column(s), or
set of rows of multiple {{FROM}} items providing the columns, the {{LATERAL}} item is
evaluated using that row or row set's values of the columns. The resulting row(s) are joined
as usual with the rows they were computed from. This is repeated for each row or set of rows
from the column source table(s).
> A trivial example of {{LATERAL}} is
> {code:sql}
> SELECT * FROM foo, LATERAL (SELECT * FROM bar WHERE bar.id = foo.bar_id) ss;
> {code}
> *Feature ID*: T491
> [https://www.postgresql.org/docs/11/queries-table-expressions.html#QUERIES-FROM]
> [https://github.com/postgres/postgres/commit/5ebaaa49445eb1ba7b299bbea3a477d4e4c0430]



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