JavaScript: GROUP BY and HAVING with Map

SQL's GROUP BY puts rows with the same key into a group and computes an aggregate for each group. WHERE filters rows before grouping, while HAVING filters the groups after the aggregate has been computed.

JavaScript

const orders = [
  { customer: "Ada", amount: 30 },
  { customer: "Bo", amount: 20 },
  { customer: "Ada", amount: 50 },
  { customer: "Cy", amount: 5 },
  { customer: "Bo", amount: 25 },
];

const totals = new Map();
for (const order of orders) {
  totals.set(order.customer, (totals.get(order.customer) ?? 0) + order.amount);
}

const result = [...totals]
  .filter(([, sum]) => sum >= 30)
  .sort((a, b) => b[1] - a[1]);

for (const [customer, sum] of result) {
  console.log(customer + " " + sum);
}

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