Function sum 

pub fn sum<ST: Foldable, expr>(
    expr: expr,
) -> sum<ST, <expr as AsExpression<ST>>::Expression>
where
    expr: AsExpression<ST>,

Represents a SQL SUM function. This function can only take types which are Foldable.

Window Function Usage

This function can be used as window function. See WindowExpressionMethods for details

Aggregate Function Expression

This function can be used as aggregate expression. See AggregateExpressionMethods for details.

Examples

Normal function usage

assert_eq!(Ok(Some(12i64)), animals.select(sum(legs)).first(connection));

Window function

let res = animals
    .select((name, sum(legs).partition_by(id)))
    .load::<(Option<String>, Option<i64>)>(connection);

assert_eq!(
    Ok(vec![(Some("Jack".into()), Some(4)), (None, Some(8))]),
    res
);

Aggregate function expression

assert_eq!(
    Ok(Some(4i64)),
    animals
        .select(sum(legs).aggregate_filter(legs.lt(8)))
        .first(connection)
);