DynamoDB: Query Group By (Guide w/ Code Examples)

DynamoDB does not implement SQL GROUP BY. For a small dataset, scan and aggregate in application code; for recurring reports, maintain counters with Streams or query an exported dataset.

Install @aws-sdk/client-dynamodb and @aws-sdk/lib-dynamodb, use an ES module on a supported Node.js runtime, and configure an AWS Region and credentials. The examples use an existing Orders table with String keys pk and sk unless an index or timestamp key is described.

import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, ScanCommand } from "@aws-sdk/lib-dynamodb";

const ddb = DynamoDBDocumentClient.from(new DynamoDBClient({}));

const counts = new Map();
let lastKey;
do {
  const page = await ddb.send(new ScanCommand({
    TableName: "Orders",
    ProjectionExpression: "#status",
    ExpressionAttributeNames: { "#status": "status" },
    ExclusiveStartKey: lastKey,
  }));
  for (const item of page.Items ?? []) {
    if (typeof item.status === "string") counts.set(item.status, (counts.get(item.status) ?? 0) + 1);
  }
  lastKey = page.LastEvaluatedKey;
} while (lastKey && Object.keys(lastKey).length > 0);
console.log(Object.fromEntries(counts));

This counts items by a String status attribute. It reads every item and does not produce a snapshot under concurrent writes.

Reference: AWS Scan API. For related access patterns, see DynamoDB query examples.