A group window expects a time attribute for grouping in a stream environment.

[大森林]

I'm learning GroupBy Window Aggregation from document https://ci.apache.org/projects/flink/flink-docs-stable/dev/table/tableApi.html

My code is:

https://paste.ubuntu.com/p/GQqR4cqdp6/

pojo is:

https://paste.ubuntu.com/p/CF4yttTGQ4/

I got 

A group window expects a time attribute for grouping in a stream environment.

Could anyone how to fix this?

I don't know the right time of this,thanks