Exercise 2: Prolific, Popular Authors — Possible Solution
===========================================================

const groups = await prisma.post.groupBy({
  by:     ["authorId"],
  where:  { published: true },                 // rows: published posts only
  _count: { _all: true },
  _avg:   { viewCount: true },
  having: {
    authorId:  { _count: { gte: 3 } },         // groups: at least 3 posts
    viewCount: { _avg:   { gt: 50 } },         // groups: average above 50
  },
  orderBy: { _avg: { viewCount: "desc" } },
});

const users = await prisma.user.findMany({
  where:  { id: { in: groups.map((g) => g.authorId) } },
  select: { id: true, name: true },
});
const names = new Map(users.map((u) => [u.id, u.name]));

const result = groups.map((g) => ({
  author:   names.get(g.authorId) ?? "(unknown)",
  posts:    g._count._all,
  avgViews: g._avg.viewCount,
}));
console.table(result);

Example output:
  ┌─────────┬─────────┬───────┬──────────┐
  │ (index) │ author  │ posts │ avgViews │
  ├─────────┼─────────┼───────┼──────────┤
  │ 0       │ 'Grace' │ 4     │ 171.25   │
  │ 1       │ 'Ada'   │ 9     │ 91.1     │
  └─────────┴─────────┴───────┴──────────┘

WHY THIS WORKS AS AN ANSWER
------------------------------
"Published" is a condition on individual posts, so it goes in where.
"At least 3 posts" and "average above 50" are conditions on whole
groups, so they go in having — both filter on aggregate values, which
is what having allows. groupBy can't include the author, so names come
from one extra findMany with an "in" filter: two queries in total no
matter how many authors qualify.