[jira] [Created] (CALCITE-5771) Apply two different NULL semantics for CONCAT function(enabled in MySQL、Postgresql and BigQuery)

["ZheHu (Jira)" <ji...@apache.org>]

ZheHu created CALCITE-5771:
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             Summary: Apply two different NULL semantics for CONCAT function(enabled in MySQL、Postgresql and BigQuery)
                 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


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|
|Postgresql|any(cast to string)|at least 1|always return string, null is treated as empty string|
|BigQuery|string|at least 1|returns null if any argument is null, otherwise return 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 that treats NULL as empty String.




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