Function check_conflicting_windows

datafusion/sql/src/select.rs:1251–1263

If there are any multiple-defined windows, we raise an error.

(window_defs: &[NamedWindowDefinition])

// If there are any multiple-defined windows, we raise an error.
fn check_conflicting_windows(window_defs: &[NamedWindowDefinition]) -> Result<()> {
    for (i, window_def_i) in window_defs.iter().enumerate() {
        for window_def_j in window_defs.iter().skip(i + 1) {
            if window_def_i.0 == window_def_j.0 {
                return plan_err!(
                    "The window {} is defined multiple times!",
                    window_def_i.0
                );
            }
        }
    }
    Ok(())
}

/// Returns true if the expression recursively contains an `Expr::Unnest` expression
fn has_unnest_expr_recursively(expr: &Expr) -> bool {