Function unproject_window_exprs 

pub(crate) fn unproject_window_exprs(
    expr: Expr,
    windows: &[&Window],
) -> Result<Expr>

Recursively identify all Column expressions and transform them into the appropriate window expression contained in window.

For example, if expr contains the column expr “COUNT(*) PARTITION BY id” it will be transformed into an actual window expression as identified in the window node.