pepijnve opened a new issue, #15129:
URL: https://github.com/apache/datafusion/issues/15129

   ### Is your feature request related to a problem or challenge?
   
   The current window function implementation only supports constant window 
frame boundaries. This restriction is reflected in the data model as well by 
the fact that `WindowFrameBound` is defined as
   
   ```
   pub enum WindowFrameBound {
       Preceding(ScalarValue),
       CurrentRow,
       Following(ScalarValue),
   }
   ```
   
   rather than
   
   ```
   pub enum WindowFrameBound {
       Preceding(Expr),
       CurrentRow,
       Following(Expr),
   }
   ```
   
   In my particular use case I have a need for variable frame boundaries to be 
able to compute aggregates over nested sets. I'm thinking of working on a patch 
that makes the above modification to `WindowFrameBound` and pushes the check 
that the `Expr` is actually a `Expr::Literal` down to the planning stage. Is 
that a change that would be acceptable?
   
   ### Describe the solution you'd like
   
   Adjust `WindowFrameBound` from
   
   ```
   pub enum WindowFrameBound {
       Preceding(ScalarValue),
       CurrentRow,
       Following(ScalarValue),
   }
   ```
   
   to
   
   ```
   pub enum WindowFrameBound {
       Preceding(Expr),
       CurrentRow,
       Following(Expr),
   }
   ```
   
   and check for `Expr::Literal` during planning.
   
   ### Describe alternatives you've considered
   
   None; open to other suggestions.
   
   ### Additional context
   
   _No response_


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