Method push_select

prqlc/prqlc/src/semantic/lowering.rs:658–717

Append a Select of final table columns derived from frame

(
        &mut self,
        lineage: Option<Lineage>,
        transforms: &mut Vec<Transform>,
    )

    /// Append a Select of final table columns derived from frame
    fn push_select(
        &mut self,
        lineage: Option<Lineage>,
        transforms: &mut Vec<Transform>,
    ) -> Result<Vec<RelationColumn>> {
        let lineage = lineage.unwrap_or_default();

        log::debug!("push_select of a frame: {lineage:?}");

        let mut columns = Vec::new();

        // normal columns
        for col in &lineage.columns {
            match col {
                LineageColumn::Single {
                    name,
                    target_id,
                    target_name,
                } => {
                    let cid = self.lookup_cid(*target_id, target_name.as_ref())?;

                    let name = name.as_ref().map(|i| i.name.clone());
                    columns.push((RelationColumn::Single(name), cid));
                }
                LineageColumn::All { input_id, except } => {
                    let Some(input) = lineage.find_input(*input_id) else {
                        return Err(Error::new_simple(
                            "column references a table not accessible in this context",
                        )
                        .push_hint("join is not supported inside group"));
                    };

                    match &self.node_mapping[&input.id] {
                        LoweredTarget::Compute(_cid) => unreachable!(),
                        LoweredTarget::Input(input_cols) => {
                            let mut input_cols = input_cols
                                .iter()
                                .filter(|(c, _)| match c {
                                    RelationColumn::Single(Some(name)) => !except.contains(name),
                                    _ => true,
                                })
                                .collect_vec();
                            input_cols.sort_by_key(|e| e.1 .1);

                            for (col, (cid, _)) in input_cols {
                                columns.push((col.clone(), *cid));
                            }
                        }
                    }
                }
            }
        }

        let (cols, cids) = columns.into_iter().unzip();

        log::debug!("... cids={cids:?}");
        transforms.push(Transform::Select(cids));