[CALCITE-5745] CONCAT2 function (enabled in Oracle library) gets wrong result when one of the arguments is NULL - ASF JIRA

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Tested CONCAT function in Oracle and got the corresponding results.

select concat('a', cast(null as varchar(20))) from DUAL;
--- results in 'a'

select concat('a', null) from DUAL;
select 'a' ||  null from DUAL;
--- both result in 'a'

In Calcite(see checkConcat2Func() in SqlOperatorTest.java), CONCAT2 function gets null when running:

concat('a', cast(null as varchar))

is related to

CALCITE-815 Add an option to allow empty strings to represent null values

CALCITE-5741 Add CONCAT_WS function (enabled in MSSQL, MySQL, Postgres libraries)

links to

GitHub Pull Request #3241