Jark Wu created CALCITE-1472:
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Summary: Support CROSS/OUTER APPLY syntax
Key: CALCITE-1472
URL: https://issues.apache.org/jira/browse/CALCITE-1472
Project: Calcite
Issue Type: New Feature
Reporter: Jark Wu
Assignee: Julian Hyde
The CROSS/OUTER APPLY is very similar to CROSS JOIN and OUTER JOIN. The
difference is that the APPLY operator is used to invoke a table-valued
function. This is not a standard SQL syntax , but introduced from MS SQL Server
[1].
The APPLY operator can be expressed by Calcite’s LATERAL TABLE . That means the
SELECT MyTable.*, t.s FROM MyTable CROSS APPLY split(MyTable.a)) AS t(s)
corresponds to :
SELECT MyTable.*, t.s FROM MyTable, LATERAL TABLE(split(MyTable.a)) AS t(s)
and
SELECT MyTable.*, t.s FROM MyTable OUTER APPLY split(MyTable.a)) AS t(s)
corresponds to:
SELECT MyTable.*, t.s FROM MyTable LEFT JOIN LATERAL TABLE(split(MyTable.a)) AS
t(s) ON TRUE
The ON TRUE part is necessary for LEFT JOIN, but it's trivial for users. That's
why I'm introducing "CROSS/OUTER APPLY" which will simplify the SQL a lot.
As the APPLY can be expressed by LATERAL, so the only thing we need to touch is
the Parser (see [2] and search FLINK to find the modification).
[1] https://technet.microsoft.com/en-us/library/ms175156(v=sql.105).aspx
[2]
https://github.com/wuchong/flink/blob/60812e51156ec9fa6088154d2f6dea8c1ff9ac17/flink-libraries/flink-table/src/main/codegen/templates/Parser.jj
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