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https://issues.apache.org/jira/browse/CALCITE-5548?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17698488#comment-17698488
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Askar Bozcan commented on CALCITE-5548:
---------------------------------------
Requested changes have been made.
Regarding tests, a test already existed for SqlParserTest, and added one to
SqlOperatorTest. When it comes to SqlOperatorTest, however, since 'style'
operand is a literal, it fails due to the way queries for tests are built
(SELECT from columns, instead of usage of values directly). Hence, the tests
for 3rd 'style' operand is moved into its own test and @Disabled.
> Add support for MSSQL CONVERT function
> --------------------------------------
>
> Key: CALCITE-5548
> URL: https://issues.apache.org/jira/browse/CALCITE-5548
> Project: Calcite
> Issue Type: Improvement
> Reporter: Askar Bozcan
> Assignee: Askar Bozcan
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Add support for MSSQL CONVERT function (which is the same as CAST, with
> optional formatting)
> More info:
> [https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-ver16]
> Example usage:
> {{SELECT CONVERT(DATETIME, '2017-08-25', 101)}}
> PR TEXT:
> This PR adds partial support for [MSSQL CONVERT
> function|https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-ver16].
> A function very similar to CAST that has an optional "style" operand to
> support different kinds of date string formats, float decimal points in
> string form, etc.
> The reason this PR is "partial", is because it simply adds a thin wrapper
> around CAST operator and does not implement anything related to 'style'
> operand other than allowing for its parsing.
> *Implemented*
> * Add lookahead in parser to first token to make sure there are no clashes
> with other unrelated CONVERT functions (including MSSQL CONVERT func)
> * Add parser rule specifically for CONVERT to add support for its syntax
> * SQLOperator (SqlConvertMssqlFunction) which utilizes
> SqlOperator.rewriteCall() to delegate all the functionality to CAST
> * Related Quidem tests in functions.iq
> *Not implemented*
> * 'style' operand is ignored. It is parsed, however beyond that, any
> functionality related to it is not implemented.
> *Difficulties & notes on implementing 'style' operator*
> Almost everywhere in the codebase, the operand order for CAST is hard-coded,
> which is not a bad assumption at all; yet because of it it seems impossible
> to fully implement CONVERT unless it's properly added as its own operator.
> For reference on CAST-related functionality:
> [RexImpTable.CastImplementor|https://github.com/apache/calcite/blob/ee9b80b0b68d442991dfaa142722e3488ec73e79/core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java#L2918]
> [StandardConvertletTable.convertCast|https://github.com/apache/calcite/blob/ee9b80b0b68d442991dfaa142722e3488ec73e79/core/src/main/java/org/apache/calcite/sql2rel/StandardConvertletTable.java#L595]
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