Query DynamoDB with standard SQL.

// DynamoDB SDK  - query two tables, join manually
const orders = await client.query({
  TableName: 'Orders',
  IndexName: 'userId-index',
  KeyConditionExpression:
    'userId = :uid AND createdAt > :d',
  FilterExpression: '#s = :status',
  ExpressionAttributeNames:
    { '#s': 'status' },
  ExpressionAttributeValues: {
    ':uid':    { S: userId },
    ':d':      { S: cutoff },
    ':status': { S: 'pending' }
  }
});

// Second query  - get customer names
const customerIds = orders.Items
  .map(o => o.customerId.S);
const customers = await client.batchGetItem({
  RequestItems: {
    'Customers': {
      Keys: customerIds.map(id => ({
        customerId: { S: id }
      }))
    }
  }
});

// Stitch results together in app code
const merged = orders.Items.map(o => ({
  ...o,
  customerName: customers.Responses
    ['Customers']
    .find(c =>
      c.customerId.S === o.customerId.S
    )?.name?.S
}));