Method calculate_range_rows

datafusion/expr/src/window_state.rs:191–243

This function calculates beginning/ending indices for the frame of the current row.

(
        window_frame: &Arc<WindowFrame>,
        length: usize,
        idx: usize,
    )

    /// This function calculates beginning/ending indices for the frame of the current row.
    fn calculate_range_rows(
        window_frame: &Arc<WindowFrame>,
        length: usize,
        idx: usize,
    ) -> Result<Range<usize>> {
        let start = match window_frame.start_bound {
            // UNBOUNDED PRECEDING
            WindowFrameBound::Preceding(ScalarValue::UInt64(None)) => 0,
            WindowFrameBound::Preceding(ScalarValue::UInt64(Some(n))) => {
                idx.saturating_sub(n as usize)
            }
            WindowFrameBound::CurrentRow => idx,
            // UNBOUNDED FOLLOWING
            WindowFrameBound::Following(ScalarValue::UInt64(None)) => {
                return internal_err!(
                    "Frame start cannot be UNBOUNDED FOLLOWING '{window_frame:?}'"
                );
            }
            WindowFrameBound::Following(ScalarValue::UInt64(Some(n))) => {
                std::cmp::min(idx + n as usize, length)
            }
            // ERRONEOUS FRAMES
            WindowFrameBound::Preceding(_) | WindowFrameBound::Following(_) => {
                return internal_err!("Rows should be UInt64");
            }
        };
        let end = match window_frame.end_bound {
            // UNBOUNDED PRECEDING
            WindowFrameBound::Preceding(ScalarValue::UInt64(None)) => {
                return internal_err!(
                    "Frame end cannot be UNBOUNDED PRECEDING '{window_frame:?}'"
                );
            }
            WindowFrameBound::Preceding(ScalarValue::UInt64(Some(n))) => {
                if idx >= n as usize {
                    idx - n as usize + 1
                } else {
                    0
                }
            }
            WindowFrameBound::CurrentRow => idx + 1,
            // UNBOUNDED FOLLOWING
            WindowFrameBound::Following(ScalarValue::UInt64(None)) => length,
            WindowFrameBound::Following(ScalarValue::UInt64(Some(n))) => {
                std::cmp::min(idx + n as usize + 1, length)
            }
            // ERRONEOUS FRAMES
            WindowFrameBound::Preceding(_) | WindowFrameBound::Following(_) => {
                return internal_err!("Rows should be UInt64");
            }
        };
        Ok(Range { start, end })
    }
}

/// State for each unique partition determined according to PARTITION BY column(s)