How is the partition date field transformed into an integer on the disk storage directory

[Lei Wang]

Create a table partitioned by event_date like this:
      `event_date` date NOT NULL COMMENT 'accurate to one day'
       PARTITION BY (event_date)

FlinkSQL consumes kafka and writes to this table. Kafka data is json format
like this: {"event_date":"2025-08-11"}

The table data is finally persisted to Minio.
But when I view the directory structure of MinIO, it is like this:

event_date=20300/
event_date=20301/
event_date=20302/

I  want to know by what rule was the date transformed into an integer?

Thanks,
Lei