DynamoDB: Query Count (Guide w/ Code Examples)

Select COUNT returns the number of matches in one response, not the total for the entire query. Sum Count while paginating; COUNT still consumes read capacity.

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, QueryCommand } from "@aws-sdk/lib-dynamodb";

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

let count = 0;
let lastKey;
do {
  const page = await ddb.send(new QueryCommand({
    TableName: "Orders",
    KeyConditionExpression: "#pk = :pk",
    ExpressionAttributeNames: { "#pk": "pk" },
    ExpressionAttributeValues: { ":pk": "CUSTOMER#123" },
    Select: "COUNT",
    ExclusiveStartKey: lastKey,
  }));
  count += page.Count ?? 0;
  lastKey = page.LastEvaluatedKey;
} while (lastKey && Object.keys(lastKey).length > 0);
console.log(count);

With a filter, Count counts returned matches and ScannedCount counts evaluated items. Approximate table ItemCount is a different metric and is not an exact real-time count.

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