Lesson 8.3: Aggregations

Aggregating over results

Suppose that we want to count the promotions each book is in rather than listing them all out by name. To do so, we can use an aggregation, as in the following query.

match
$book isa book;
$promotion isa promotion;
($book, $promotion);
reduce $promotion_count = count groupby $book;
fetch { "title": $book.title, "promotions": $promotion_count };

You can aggregate the entire answer stream, or groupby variables to compute per-group metrics. See Reduce.

Exercise

Retrieve a list of publishers. For each publisher, retrieve their name and the number of books they have published.

You may find it useful to refer to the bookstore’s schema.

Schema 
define

entity book @abstract,
    owns isbn @card(0..2),
    owns isbn-13 @key,
    owns isbn-10 @unique,
    owns title,
    owns page-count,
    owns genre @card(0..),
    owns price,
    plays contribution:work,
    plays publishing:published,
    plays promotion-inclusion:item,
    plays order-line:item,
    plays rating:rated,
    plays recommendation:recommended;

entity hardback sub book,
    owns stock;

entity paperback sub book,
    owns stock;

entity ebook sub book;

entity contributor,
    owns name,
    plays contribution:contributor,
    plays authoring:author,
    plays editing:editor,
    plays illustrating:illustrator;

entity company @abstract,
    owns name;

entity publisher sub company,
    plays publishing:publisher;

entity courier sub company,
    plays delivery:deliverer;

entity publication,
    owns year,
    plays publishing:publication,
    plays locating:located;

entity user,
    owns id @key,
    owns name,
    owns birth-date,
    plays action-execution:executor,
    plays locating:located,
    plays recommendation:recipient;

entity order,
    owns id @key,
    owns status,
    plays order-line:order,
    plays action-execution:action,
    plays delivery:delivered;

entity promotion,
    owns code @key,
    owns name,
    owns start-timestamp,
    owns end-timestamp,
    plays promotion-inclusion:promotion;

entity review,
    owns id @key,
    owns score,
    owns verified,
    plays rating:review,
    plays action-execution:action;

entity login,
    owns success,
    plays action-execution:action;

entity address,
    owns street,
    plays delivery:destination,
    plays locating:located;

entity place @abstract,
    owns name,
    plays locating:located,
    plays locating:location;

entity city sub place;

entity state sub place;

entity country sub place;

relation contribution,
    relates contributor,
    relates work;

relation authoring sub contribution,
    relates author as contributor;

relation editing sub contribution,
    relates editor as contributor;

relation illustrating sub contribution,
    relates illustrator as contributor;

relation publishing,
    relates publisher,
    relates published,
    relates publication;

relation promotion-inclusion,
    relates promotion,
    relates item,
    owns discount;

relation order-line,
    relates order,
    relates item,
    owns quantity,
    owns price;

relation rating,
    relates review,
    relates rated;

relation action-execution,
    relates action,
    relates executor,
    owns timestamp;

relation delivery,
    relates deliverer,
    relates delivered,
    relates destination;

relation locating,
    relates located,
    relates location;

relation recommendation,
    relates recommended,
    relates recipient;

attribute isbn @abstract, value string;
attribute isbn-13 sub isbn;
attribute isbn-10 sub isbn;
attribute title, value string;
attribute page-count, value integer;
attribute genre, value string;
attribute stock, value integer;
attribute price, value double;
attribute discount, value double;
attribute id, value string;
attribute code, value string;
attribute name, value string;
attribute birth-date, value datetime;
attribute street, value string;
attribute year, value integer;
attribute quantity, value integer;
attribute score, value integer;
attribute verified, value boolean;
attribute timestamp, value datetime;
attribute start-timestamp, value datetime;
attribute end-timestamp, value datetime;
attribute status, value string @regex("^(paid|dispatched|delivered|returned|canceled)$");
attribute success, value boolean;

# TODO: Change to check
fun is_review_verified_by_purchase($review: review) -> { order }:
  match
    ($review, $product) isa rating;
    ($order, $product) isa order-line;
    ($user, $review) isa action-execution, has timestamp $review-time;
    ($user, $order) isa action-execution, has timestamp $order-time;
    $review-time > $order-time;
  return { $order };

fun book_recommendations_for($user: user) -> {book}:
  match
    $new-book isa book;
    {
        let $new-book in book_recommendations_by_author($user);
    } or {
        let $new-book in book_recommendations_by_genre($user);
    };
  return { $new-book };

fun book_recommendations_by_genre($user: user) -> { book }:
match
    $user isa user;
    $liked-book isa book;
    {
        ($user, $order-for-liked) isa action-execution;
        ($order-for-liked, $liked-book) isa order-line;
    } or {
        ($user, $review-for-liked) isa action-execution;
        ($review-for-liked, $liked-book) isa rating;
        $review-for-liked has score >= 7;
    };
    $new-book isa book;
    not { {
        ($user, $order-for-new) isa action-execution;
        ($order-for-new, $new-book) isa order-line;
    } or {
        ($user, $review-for-new) isa action-execution;
        ($review-for-new, $new-book) isa rating;
    }; };
    $liked-book has genre $shared-genre;
    $new-book has genre $shared-genre;
    not { {
        $shared-genre == "fiction";
    } or {
        $shared-genre == "nonfiction";
    }; };
  return { $new-book };

fun book_recommendations_by_author($user: user) -> { book }:
  match
    $user isa user;
    $liked-book isa book;
    {
        ($user, $order-for-liked) isa action-execution;
        ($order-for-liked, $liked-book) isa order-line;
    } or {
        ($user, $review-for-liked) isa action-execution;
        ($review-for-liked, $liked-book) isa rating;
        $review-for-liked has score >= 7;
    };
    $new-book isa book;
    not { {
        ($user, $order-for-new) isa action-execution;
        ($order-for-new, $new-book) isa order-line;
    } or {
        ($user, $review-for-new) isa action-execution;
        ($review-for-new, $new-book) isa rating;
    }; };
    ($liked-book, $shared-author) isa authoring;
    ($new-book, $shared-author) isa authoring;
  return { $new-book };

fun order_line_best_price($line: order-line) -> { double }:
  match
    ($order) isa action-execution, has timestamp $order-time;
    $line isa order-line, links ($order, $item);
    $item has price $retail-price;
    let $time_value = $order-time;
    let $best-discount = best_discount_for_item($item, $time_value);
    let $discounted-price = round(100 * $retail-price * (1 - $best-discount)) / 100;
    $line has quantity $quantity;
    let $line-total = $quantity * $discounted-price;
  return { $line-total };

fun best_discount_for_item($item: book, $order-time: datetime) -> double:
  match
    {
        $inclusion isa promotion-inclusion,
            links ($promotion, $item),
            has discount $discount-attr;
        $promotion has start-timestamp <= $order-time,
            has end-timestamp >= $order-time;
        let $discount = $discount-attr;
    } or {
        let $discount = 0.0; # default
    };
return max($discount);

fun transitive_places($place: place) -> { place }:
  match
    {
      locating (located: $place, location: $parent);
    } or {
      locating (located: $place, location: $middle);
      let $parent in transitive_places($middle);
    };
  return { $parent };
Sample solution 
match
$publisher isa publisher;
$book isa book;
publishing ($book, $publisher);
reduce $published = count groupby $publisher;
fetch {
  "publisher": $publisher.name,
  "books-published": $published,
};

Aggregation modifiers

We have seen an example of the count modifier, and now we will explore examples of some of the others. The table below lists the aggregation modifiers currently available in TypeQL.

Aggregation modifier Name Takes argument

count

Count

No

sum

Sum

Yes

max

Maximum

Yes

min

Minimum

Yes

mean

Mean

Yes

median

Median

Yes

std

Standard deviation

Yes

The std modifier returns the sample standard deviation as obtained by Bessel’s correction.

Unlike the count modifier, the other aggregation modifiers all take a variable as an argument. Let’s see an example. In the following query, we retrieve the average review score for each book.

match
$book isa book;
$review isa review, has score $score;
rating ($review, $book);
reduce $avg_score = mean($score) groupby $book;
fetch { "title": $book.title, "average-score": $avg_score };

Whereas the count modifier returns the number of results matched regardless of their content, the other aggregation modifiers require a specified numeric value to operate over. Here, we have supplied the $score attribute as the argument to the mean modifiers, indicating that we want the average of its values.

match
$order isa order, has id $id;
$book isa book, has price $retail_price;
order-line ($order, $book), has quantity $quantity;
let $line_total = $quantity * $retail_price;
reduce $order_total = sum($line_total) groupby $id;
fetch { "id": $id, "order-total": $order_total };