1.3.3 Query vs Scan

import boto3
from boto3.dynamodb.conditions import Key

table = boto3.resource('dynamodb').Table('Orders')

# Query by PK + SK range
response = table.query(
    KeyConditionExpression=Key('user_id').eq('user-123') &
                           Key('order_date').between('2025-01-01', '2025-12-31'),
    ScanIndexForward=False,  # Descending order
    Limit=10
)

# Scan toàn bộ table (EXPENSIVE!)
response = table.scan(
    FilterExpression=Attr('status').eq('active'),
    ProjectionExpression='id, #n, email',
    ExpressionAttributeNames={'#n': 'name'}  # 'name' là reserved word
)

import concurrent.futures

def scan_segment(segment, total_segments):
    return table.scan(
        Segment=segment,
        TotalSegments=total_segments,
        FilterExpression=Attr('status').eq('active')
    )

# Scan song song 4 segments
with concurrent.futures.ThreadPoolExecutor() as executor:
    futures = [executor.submit(scan_segment, i, 4) for i in range(4)]