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https://issues.apache.org/jira/browse/CALCITE-5570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17699381#comment-17699381
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Sergey Nuyanzin commented on CALCITE-5570:
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There is not much engines supporting maps which I was able to find
At least within what I found more tend to use angle brackets
*Angle* brackets for map:
Vertica:
[https://www.vertica.com/docs/11.0.x/HTML/Content/Authoring/SQLReferenceManual/DataTypes/SET.htm#Casting]
seems Vertica does not have a generic approach since
it uses angle brackets for maps and square brackets for arrays
Databricks:
[https://docs.databricks.com/sql/language-manual/data-types/map-type.html#examples]
Spark:
[https://spark.apache.org/docs/latest/api/sql/index.html#typeof]
in Spark it is not clear from doc that it supports
cast to map/array, looks like no. However they return result of typeof with
angle brackets.
Flink:
[https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/types/#map]
*Round* for map:
ClickHouse: [https://clickhouse.com/docs/en/sql-reference/data-types/map/]
> Support nested map type for SqlDataTypeSpec
> -------------------------------------------
>
> Key: CALCITE-5570
> URL: https://issues.apache.org/jira/browse/CALCITE-5570
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Sergey Nuyanzin
> Assignee: Jiajun Xie
> Priority: Major
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> There was added a similar support for arrays/multisets at
> https://issues.apache.org/jira/browse/CALCITE-3250
> however there is no support for maps so far.
> The issue is to add such support.
>
> I think I'd like to clarify is syntax for maps since it has 2 internal
> subtypes for keys and values may be something similar to ROW with delimiter
> like
> {code:sql}
> SELECT CAST(NULL AS MAP(INT, INT));
> -- or with square brackets similar to map constructor
> SELECT CAST(NULL AS MAP[INT, INT]);
> -- or with angle (Flink syntax)
> SELECT CAST(NULL AS MAP<INT, INT>);
> {code}
>
>
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