Function unproject_agg_exprs

datafusion/sql/src/unparser/utils.rs:222–246

Recursively identify all Column expressions and transform them into the appropriate aggregate expression contained in agg. For example, if expr contains the column expr "COUNT(*)" it will be transformed into an actual aggregate expression COUNT(*) as identified in the aggregate node.

(
    expr: Expr,
    agg: &Aggregate,
    windows: Option<&[&Window]>,
)

/// For example, if expr contains the column expr "COUNT(*)" it will be transformed
/// into an actual aggregate expression COUNT(*) as identified in the aggregate node.
pub(crate) fn unproject_agg_exprs(
    expr: Expr,
    agg: &Aggregate,
    windows: Option<&[&Window]>,
) -> Result<Expr> {
    expr.transform(|sub_expr| {
            if let Expr::Column(c) = sub_expr {
                if let Some(unprojected_expr) = find_agg_expr(agg, &c)? {
                    Ok(Transformed::yes(unprojected_expr.clone()))
                } else if let Some(unprojected_expr) =
                    windows.and_then(|w| find_window_expr(w, &c.name).cloned())
                {
                    // Window function can contain an aggregation columns, e.g., 'avg(sum(ss_sales_price)) over ...' that needs to be unprojected
                    Ok(Transformed::yes(unproject_agg_exprs(unprojected_expr, agg, None)?))
                } else {
                    internal_err!(
                        "Tried to unproject agg expr for column '{}' that was not found in the provided Aggregate!", &c.name
                    )
                }
            } else {
                Ok(Transformed::no(sub_expr))
            }
        })
        .map(|e| e.data)
}

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