Github user buptljy commented on the issue:
https://github.com/apache/flink/pull/5615
Actually I am not sure if it is appropriate to return "string" because it
should be the inverse of the "DATE_FORMAT()". However, If I return
DATE/TIME/DATETIME as the jira issue described, the type of data user receives
will be uncertain in one of DATE/TIME/DATETIME.
Do you have some good ideas ? I will optimize it.---
