Exercise 1: Posts Per Month — Possible Solution
=================================================

type MonthRow = { month: number; posts: number };

app.get("/stats/monthly", async (req, res) => {
  const year = new Date().getFullYear();
  const start = new Date(year, 0, 1);
  const end   = new Date(year + 1, 0, 1);

  const rows = await prisma.$queryRaw<MonthRow[]>`
    SELECT EXTRACT(MONTH FROM "createdAt")::int AS "month",
           COUNT(*)::int                        AS "posts"
    FROM "Post"
    WHERE "published" = true
      AND "createdAt" >= ${start} AND "createdAt" < ${end}
    GROUP BY 1
    ORDER BY 1
  `;

  res.json(rows);
});

  $ curl localhost:3000/stats/monthly
  [{"month":3,"posts":2},{"month":6,"posts":5},{"month":9,"posts":4}]

The alternative fix, if you'd rather not cast in SQL:

  res.json(rows.map((r) => ({ month: Number(r.month), posts: Number(r.posts) })));

WHY THIS WORKS AS AN ANSWER
------------------------------
Grouping by month isn't something Prisma Client's groupBy can do — it
groups by stored fields, not by values computed from them — so raw SQL
is the right tool. The dates are passed as parameters, not pasted into
the SQL. On PostgreSQL COUNT(*) returns bigint (and EXTRACT returns a
numeric), which would reach JavaScript as bigint/Decimal; the ::int
casts turn them into plain numbers, so res.json works. Using a
start/end range instead of EXTRACT(YEAR ...) in WHERE also lets the
database use an index on createdAt.