Cannot select aggregate and non-aggregate fields

[jasonl]

With a table

table! {
    mrr_by_date (account_id, date) {
        account_id -> Integer,
        date -> Date,
        mrr -> Double,
    }
}

I cannot do:

mrr_by_date
            .group_by(date)
            .select((sum(mrr), date))
            .filter(account_id.eq(123))

Because I get the following error:

149 |             .select((sum(mrr), date))
    |              ^^^^^^ the trait `diesel::SelectableExpression<models::mrr_by_date::mrr_by_date::table, _>` is not implemented for `(diesel::expression::Sum<models::mrr_by_date::mrr_by_date::columns::mrr>, models::mrr_by_date::mrr_by_date::columns::date)`
    |
    = help: the following implementations were found:
    = help:   <(A, B) as diesel::SelectableExpression<QS, (SA, SB)>>
    = help:   <(A, B) as diesel::SelectableExpression<QS, diesel::types::Nullable<(SA, SB)>>>
    = note: required because of the requirements on the impl of `diesel::query_builder::Query` for `diesel::query_builder::SelectStatement<_, (diesel::expression::Sum<models::mrr_by_date::mrr_by_date::columns::mrr>, models::mrr_by_date::mrr_by_date::columns::date), models::mrr_by_date::mrr_by_date::table, diesel::query_builder::distinct_clause::NoDistinctClause, diesel::query_builder::where_clause::NoWhereClause, diesel::query_builder::order_clause::NoOrderClause, diesel::query_builder::limit_clause::NoLimitClause, diesel::query_builder::offset_clause::NoOffsetClause, diesel::query_builder::group_by_clause::GroupByClause<models::mrr_by_date::mrr_by_date::columns::date>>`
    = note: required because of the requirements on the impl of `diesel::SelectDsl<(diesel::expression::Sum<models::mrr_by_date::mrr_by_date::columns::mrr>, models::mrr_by_date::mrr_by_date::columns::date), _>` for `diesel::query_builder::SelectStatement<(diesel::types::Integer, diesel::types::Date, diesel::types::Double), (models::mrr_by_date::mrr_by_date::columns::account_id, models::mrr_by_date::mrr_by_date::columns::date, models::mrr_by_date::mrr_by_date::columns::mrr), models::mrr_by_date::mrr_by_date::table, diesel::query_builder::distinct_clause::NoDistinctClause, diesel::query_builder::where_clause::NoWhereClause, diesel::query_builder::order_clause::NoOrderClause, diesel::query_builder::limit_clause::NoLimitClause, diesel::query_builder::offset_clause::NoOffsetClause, diesel::query_builder::group_by_clause::GroupByClause<models::mrr_by_date::mrr_by_date::columns::date>>`

(I have edited the code and error messages slightly to remove what I believe is non-relevant information, am happy to share the full error messages privately).

Am I reading this correctly as there isn't support for combining aggregate and non-aggregate fields in a select statement, despite the SQL intended to be produced being valid:

SELECT sum(mrr), date FROM mrr_by_date WHERE account_id = $1 GROUP BY date

Or am I doing something wrong here?

[sgrif]

No, you're doing nothing wrong. We don't fully support group by yet. See #210 and #3