Support common aggregate queries

[billy1624]

Motivation

Be able to querying of common aggregation on a column.

Proposed Solutions

• Aggregate at root

query {
  postAggregate(filter: {  # Generate a query with name `<Entity>Aggregate` for each entity
    title: {
        anyofterms: "GraphQL"
      }
  }) {
    count  # COUNT(*)
    numLikesMax  # MAX(num_likes)
    numLikesMin  # MIN(num_likes)
    numLikesSum  # SUM(num_likes)
    numLikesAvg  # AVG(num_likes)
  }
}

• Aggregate at child

query {
  author {
    name
    postAggregate(filter: {  # Generate a query with name `<Entity>Aggregate` for each related entity
      title: {
          anyofterms: "GraphQL"
        }
    }) {
      count  # COUNT(*)
      numLikesMax  # MAX(num_likes)
      numLikesMin  # MIN(num_likes)
      numLikesSum  # SUM(num_likes)
      numLikesAvg  # AVG(num_likes)
    }
  }
}

Additional Information

Similar API is provided on Dgraph:

• https://dgraph.io/docs/graphql/queries/aggregate