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https://issues.apache.org/jira/browse/SPARK-34382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17329394#comment-17329394
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Apache Spark commented on SPARK-34382:
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User 'allisonwang-db' has created a pull request for this issue:
https://github.com/apache/spark/pull/32303
> ANSI SQL: LATERAL derived table(T491)
> -------------------------------------
>
> Key: SPARK-34382
> URL: https://issues.apache.org/jira/browse/SPARK-34382
> 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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