Aggregate + non-aggregate expressions not allowed where they should be

[SteelAlloy]

Setup

Versions

• Rust: 1.66.0
• Diesel: 2.0.3
• Database: PostgreSQL
• Operating System: Linux

Feature Flags

• diesel: ["uuid", "postgres", "r2d2", "numeric", "chrono", "serde_json"]

Problem Description

The following query gives some errors, mixing aggregate and non-aggregate expressions

diesel::table! {
    foo (uuid, date) {
        uuid -> Uuid,
        date -> Date,
    }
}

foo::table
        .select((foo::uuid, diesel::dsl::max(foo::date)))
        .group_by(foo::uuid)

What are you trying to accomplish?

I'm trying to translate this valid SQL query to diesel dsl

CREATE TABLE foo (
    uuid uuid PRIMARY KEY NOT NULL,
    date timestamp DEFAULT now() NOT NULL
);

SELECT uuid, max(date) date FROM foo GROUP BY uuid;

What is the expected output?

Being able to mix such expressions when it's valid sql

What is the actual output?

error[E0277]: the trait bound `diesel::expression::is_aggregate::No: MixedAggregates<diesel::expression::is_aggregate::Yes>` is not satisfied
   --> src/graphql/entities/user.rs:392:10
    |
392 |         .select((foo::uuid_1, diesel::dsl::max(foo::date)))
    |          ^^^^^^ the trait `MixedAggregates<diesel::expression::is_aggregate::Yes>` is not implemented for `diesel::expression::is_aggregate::No`
    |
    = help: the following other types implement trait `MixedAggregates<Other>`:
              <diesel::expression::is_aggregate::No as MixedAggregates<diesel::expression::is_aggregate::Never>>
              <diesel::expression::is_aggregate::No as MixedAggregates<diesel::expression::is_aggregate::No>>
    = note: required for `(db::schema::foo::columns::uuid_1, diesel::expression::functions::aggregate_ordering::max::max<diesel::sql_types::Date, db::schema::foo::columns::date>)` to implement `ValidGrouping<()>`
    = note: required for `SelectStatement<FromClause<db::schema::foo::table>>` to implement `SelectDsl<(db::schema::foo::columns::uuid_1, diesel::expression::functions::aggregate_ordering::max::max<diesel::sql_types::Date, db::schema::foo::columns::date>)>`

Are you seeing any additional errors?

No, many thanks for your hard work

Steps to reproduce

Checklist

• I have already looked over the issue tracker and the disussion forum for similar possible closed issues.

If you are unsure if your issue is a duplicate of an existing issue please link the issue in question here

• Aggregate + non-aggregate expressions can be mixed in places where they should not be allowed to #1586

• This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)

• This issue can be reproduced without requiring a third party crate

[weiznich]

This is "expected" as we assume that the call to the group_by function appears before the select call. This assumption is made to have somewhat clearer error messages here (so that they point at least to the .select() call instead of only pointing at the query). So for reference the following query compiles:

foo::table
        .group_by(foo::uuid)
        .select((foo::uuid, diesel::dsl::max(foo::date)))

That written: I just checked the documentation and it does not mention this restriction at all. We should probably have that in the documentation of .select and .group_by. So that's at least a missing/bad documentation bug.

[SteelAlloy]

Thanks, it does indeed work better in this order
I can add this to the documentation if I have time