The window function in the standard database only supports the "over" window, such as `LAG`,` LEAD`, `FIRST_VALUE`,` LAST_VALUE`. These window functions do not apply to `Slide`,` Tumble`, `Session` window. So when the user-defined AGG need to be clearly defined. In calcite `SqlAggFunction` will using `requiresOver` to distinguish.
In this JIRA. will deal with this feature.