task Join fan-out & cardinality · hard

Compare category audience overlap

For each alphabetically ordered pair of categories sharing at least one delivered-order shopper, return shared_buyers, union_buyers and jaccard = shared / union rounded to three decimals.

what to return

Columns

category_acategory_bshared_buyersunion_buyersjaccard in this order

Rows

6 rows · in the order asked

Watch for

A shopper belongs to a category once, regardless of repeat orders or quantities. Include only pairs with shared buyers.

Use category_a < category_b. Order by category_a,category_b.

Skill

Compute Jaccard overlap without inflating membership by line-item or repeat-order counts. Refresher: Multi-grain joins without fan-out →

expected result

Your query should return exactly these columns and values. Run it and compare.

data you can query

Sample rows from each table. Each column shows its type underneath; → marks a link to another table.