Function join_table_borders

datafusion/physical-plan/src/projection.rs:909–935

Returns the last index before encountering a column coming from the right table when traveling through the projection from left to right, and the last index before encountering a column coming from the left table when traveling through the projection from right to left. If there is no column in the projection coming from the left side, it returns (-1, ...), if there is no column in the projection

(
    left_table_column_count: usize,
    projection_as_columns: &[(Column, String)],
)

/// If there is no column in the projection coming from the left side, it returns (-1, ...),
/// if there is no column in the projection coming from the right side, it returns (..., projection length).
pub fn join_table_borders(
    left_table_column_count: usize,
    projection_as_columns: &[(Column, String)],
) -> (i32, i32) {
    let far_right_left_col_ind = projection_as_columns
        .iter()
        .enumerate()
        .take_while(|(_, (projection_column, _))| {
            projection_column.index() < left_table_column_count
        })
        .last()
        .map(|(index, _)| index as i32)
        .unwrap_or(-1);

    let far_left_right_col_ind = projection_as_columns
        .iter()
        .enumerate()
        .rev()
        .take_while(|(_, (projection_column, _))| {
            projection_column.index() >= left_table_column_count
        })
        .last()
        .map(|(index, _)| index as i32)
        .unwrap_or(projection_as_columns.len() as i32);

    (far_right_left_col_ind, far_left_right_col_ind)
}

/// Tries to update the equi-join `Column`'s of a join as if the input of
/// the join was replaced by a projection.