The following code can be improved which is introduced by
1. FlinkRelOptUtilTest#testToString shouldn't ignore attributes of RelNodes. The original expcted string makes sense. We should fix it to keep the result unchanged.
2. The test CatalogTableITCase#testInsertSinkTableWithUnmatchedFields should fail and shouldn't verify the expected results (no results).
3. SqlToOperationConverterTest#testCreateTableWithComputedColumn change the udf calling to non-qualified way to verify the qualifying works well.