Hello, everyone in the calcite community. I encountered a problem while dealing with https://issues.apache.org/jira/browse/CALCITE-6300. That is, when should the type conversions related to map and array be performed?
At present, I can think of two solutions. One is to convert the final result when returning the result, such as: https://issues.apache.org/jira/browse/CALCITE-5948, e.g: @LibraryOperator(libraries = {SPARK}) public static final SqlFunction ARRAY_COMPACT = SqlBasicFunction.create(SqlKind.ARRAY_COMPACT, SqlLibraryOperators::arrayCompactReturnType, OperandTypes.ARRAY); The second is to convert after parameter type verification, for example, https://issues.apache.org/jira/browse/CALCITE-6300 @LibraryOperator(libraries = {SPARK}) public static final SqlFunction MAP_VALUES = SqlBasicFunction.create(SqlKind.MAP_VALUES, ReturnTypes.TO_MAP_VALUES_NULLABLE, OperandTypes.MAP) .withOperandTypeInference(InferTypes.MAP_SPARK_FUNCTION_TYPE); Perhaps these two methods are not suitable, because they are not universal solutions. I don’t know how the database defines this type conversion standard, but Calcite does not seem to have a clear standard for this conversion. But I think it should be solved because many functions in Spark need this conversion. (p.s. I have implemented the adjustTypeForMapFunctionConstructor api, but I don't know where to put it.) More discussions can be viewed in jira: https://issues.apache.org/jira/browse/CALCITE-6300 If there are any mistakes in my description process, please correct me. For solutions, if others have better suggestions or other project code examples, please put them forward. I am happy to learn. Sorry for asking this question so late Best wishes, Cancai Cai
