Idea for grouping

group.graphql

###
# The result below shows the sum of population of all cities.
###
{
  Local {
    Get(where:{
      operands: [{
        path: ["Things", "City", "population"],
        operator: GreaterThan
        valueInt: 1000000
      }]
    },{
      group:{
        operands: [{
          path: ["Things", "City", "population"],
          aggregate: SUM # other options: COUNT, MAX, MIN, SUM, AVG, 
        }]
      }
    }) {
      Things {
        City {
          population
        }
      }
    }
  }
}

To me these feel like 'statistical' functions, and not 'Get' functions.
I'd argue that a separate 'Aggregated' or 'Statistics' field under Local would do wonders for keeping the 'Get' function simple.

{
  Local {
    Aggregated() {
      Things { City { .... } }
    }

    // or
    Statistics(...) {
      Things { City { .... } }
    }
  }
}

I image that such a field could be translated to Network queries too.

---

I find it hard to understand what these different aggregations are supposed to do, based on the GraphQL query.

I believe that we should distinguish between simple counts with conditions, and more complex operations like groupBy.
Each different function/operation should ideally correspond to a field below 'Aggregated' or 'Statistics'.

This will make it very simple for end users to start to do some operations.
Initial impressions count, and a initial expore to simple statistics are very good for the demo-ability of Weaviate.

Simple sum

{
  Local {
    Statistics(where: { ... }) {
      Sum {
        Things {
          City {
            population
          }
        }
      }
    }
  }
}

Output

{ "Local": { "Statistics": { "Sum": { "Things": { "City": { "population": 42 } } } } } }

95% percentile

{
  Local {
    Statistics(where: { ... }) {
      # Compute 95% range of data.
      Percentile(from: 0.25, to: 0.975) {
        Things {
          City {
            population
          }
        }
      }
    }
  }
}

Output

{ "Local": { "Statistics": { "Sum": { "Things": { "City": { "population": {
  "min": 1000,
  "max": 2000
}} } } } } }

Group By

{
  Local {
    Statistics(where: { ... }) {
      GroupBy() {
        Things {
          City {
            country @groupBy(fn: GROUP_BY)
            totalPopulation: population @groupBy(fn: SUM)
            smallestCity: population @groupBy(fn: MIN)
            biggestCity: population @groupBy(fn: MAX)
          }
        }
      }
    }
  }
}

A extra advantage of doing tis that you'll be able to clearly defend that these are different functions with different pricing than just slurping the data out of weaviate/a network.

That indeed sounds reasonable. Not necessarily in favor for one or the other but syntactically it might absolutely be preferable to introduce a Stats{} function.

Naming wise, maybe Aggregate{} would suit better. Any thoughts @laura-ham and @moretea?

It would also be possible to add all aggregation functions as GQL-functions.

{
  Local {
    Aggregate(where: { ... }) { # or Stats...
      Sum{}
      Percentile{}
      Count{}
      Average{} 
      Maximum{}
      Median{}
      Minimum{}
      Mode{}
      GroupBy() {} # Would be used for more complext group by functions.
  }
} 

@moretea would it be fair to say that splitting these aggregate functions (except for GroupBy()) would be relatively easier to implement?

Maybe they are simple to implement. I would expect so, based on my experience with SQL. However, Gremlin is not as well rounded, and I did not research this yet for Gremlin.