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https://issues.apache.org/jira/browse/CALCITE-5771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17733664#comment-17733664
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Tanner Clary commented on CALCITE-5771:
---------------------------------------
Closed in
[3f2ae2f|https://github.com/apache/calcite/commit/3f2ae2f4dd2d6b1fab7c3a91e67a6a6d28523298],
thanks for the PR [~VAE]!
> Apply two different NULL semantics for CONCAT function(enabled in MySQL,
> Postgresql, BigQuery and MSSQL)
> --------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-5771
> URL: https://issues.apache.org/jira/browse/CALCITE-5771
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.34.0
> Reporter: ZheHu
> Assignee: ZheHu
> Priority: Major
> Labels: pull-request-available
>
> We now have one CONCAT_FUNCTION which is enabled in MySQL, Postgresql,
> BigQuery, it always returns NULL when any of the arguments is NULL, and it
> accepts at least 2 arguments.
> The following table describes how different database products define CONCAT
> function:
> ||DB Product||Argument type in CONCAT||Argument num in CONCAT||Result||
> |MySQL|string|at least 1|returns null if any argument is null, otherwise
> return string|
> |BigQuery|string|at least 1|returns null if any argument is null, otherwise
> return string|
> |Postgresql|any(cast to string)|at least 1|always return string, null is
> treated as empty string|
> |MSSQL|string|2 ~ 254|always return string, null is treated as empty string|
> For MySQL and BigQuery, we can reuse the current CONCAT_FUNCTION(but need to
> change the accepted argument number). We also need another CONCAT function
> for Postgresql and MSSQL that treats NULL as empty String. And they both
> accept at least 1 argument.
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