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https://issues.apache.org/jira/browse/CALCITE-3081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16897686#comment-16897686
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Danny Chan commented on CALCITE-3081:
-------------------------------------
It solves partially, if this select statement union with another one, for
example:
{code:sql}
select null from t1
union
select a from t2 -- a is int type
{code}
with implicit type cast, we would finally got query:
{code:sql}
select cast(null as int) from t1
union
select a from t2 -- a is int type
{code}
For single select statement, we did have no way to deduce the intended type.
> Literal NULL should be generated in SqlDialect
> ----------------------------------------------
>
> Key: CALCITE-3081
> URL: https://issues.apache.org/jira/browse/CALCITE-3081
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.19.0
> Reporter: Feng Zhu
> Priority: Minor
>
> In Calcite, this simple query will throw exception during validation, even it
> is ok in many databases.
> {code:java}
> Query:
> final String query = "select NULL as col "
> + "from \"foodmart\".\"product\"";
> Exception
> org.apache.calcite.tools.ValidationException:
> org.apache.calcite.runtime.CalciteContextException: From line 1, column 8 to
> line 1, column 11: Illegal use of 'NULL'
> {code}
> The right way to use 'NULL' in Calcite is:
> {code:java}
> final String query = "select cast(NULL as integer) as col "
> + "from \"foodmart\".\"product\"";
> {code}
> However, the converted query by *RelToSqlConverter* is illegal in Calcite.
> {code:java}
> SELECT NULL AS \"COL\"
> FROM \"foodmart\".\"product\"
> {code}
> The issue is trivial, but it is against to general sense. Maybe we can
> generate NULL literal in SqlDialect?
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