假設 orders 集合有以下記錄：
[ {"_id":4,"book":"novel 1","price":30,"quantity":2}, {"_id":5,"book":"science 1","price":20,"quantity":1}, {"_id":6} ]
books 集合有以下記錄：
[ {"_id":"book1","author":"author 1","category":"novel","stock":10,"time":1564456048486,"title":"novel 1"}, {"_id":"book3","author":"author 3","category":"science","stock":30,"title":"science 1"}, {"_id":"book4","author":"author 3","category":"science","stock":40,"title":"science 2"}, {"_id":"book2","author":"author 2","category":"novel","stock":20,"title":"novel 2"}, {"_id":"book5","author":"author 4","category":"science","stock":50,"title":null}, {"_id":"book6","author":"author 5","category":"novel","stock":"60"} ]
以下聚合操作可以通過一個相等匹配條件連接 orders 和 books 集合，匹配的字段是 orders 集合的 book 字段和 books 集合的 title 字段：
const db = uniCloud.database() let res = await db.collection('orders').aggregate() .lookup({ from: 'books', localField: 'book', foreignField: 'title', as: 'bookList', }) .end()
結果：
[ { "_id": 4, "book": "novel 1", "price": 30, "quantity": 2, "bookList": [ { "_id": "book1", "title": "novel 1", "author": "author 1", "category": "novel", "stock": 10 } ] }, { "_id": 5, "book": "science 1", "price": 20, "quantity": 1, "bookList": [ { "_id": "book3", "category": "science", "title": "science 1", "author": "author 3", "stock": 30 } ] }, { "_id": 6, "bookList": [ { "_id": "book5", "category": "science", "author": "author 4", "stock": 50, "title": null }, { "_id": "book6", "author": "author 5", "stock": "60", "category": "novel" } ] } ]