Function plan_map_subquery

src/sql/src/plan/query.rs:4806–4910

(
    ecx: &ExprContext,
    query: &Query<Aug>,
)

}

fn plan_map_subquery(
    ecx: &ExprContext,
    query: &Query<Aug>,
) -> Result<CoercibleScalarExpr, PlanError> {
    if !ecx.allow_subqueries {
        sql_bail!("{} does not allow subqueries", ecx.name)
    }

    let mut qcx = ecx.derived_query_context();
    let mut query = plan_query(&mut qcx, query)?;
    if query.limit.is_some()
        || !query
            .offset
            .clone()
            .try_into_literal_int64()
            .is_ok_and(|offset| offset == 0)
    {
        query.expr = HirRelationExpr::top_k(
            query.expr,
            vec![],
            query.order_by.clone(),
            query.limit,
            query.offset,
            query.group_size_hints.limit_input_group_size,
        );
    }
    if query.project.len() != 2 {
        sql_bail!(
            "expected map subquery to return 2 columns, got {} columns",
            query.project.len()
        );
    }

    let query_types = qcx.relation_type(&query.expr).column_types;
    let key_column = query.project[0];
    let key_type = query_types[key_column].clone().scalar_type();
    let value_column = query.project[1];
    let value_type = query_types[value_column].clone().scalar_type();

    if key_type != SqlScalarType::String {
        sql_bail!("cannot build map from subquery because first column is not of type text");
    }

    let aggregation_exprs: Vec<_> = iter::once(HirScalarExpr::call_variadic(
        RecordCreate {
            field_names: vec![ColumnName::from("key"), ColumnName::from("value")],
        },
        vec![
            HirScalarExpr::column(key_column),
            HirScalarExpr::column(value_column),
        ],
    ))
    .chain(
        query
            .order_by
            .iter()
            .map(|co| HirScalarExpr::column(co.column)),
    )