如果有重复，如何对记录求和？

SELECT product_id, SUM(quantity) as total_quantity
FROM sales
GROUP BY product_id;

data = [
    {'product_id': 1, 'quantity': 5},
    {'product_id': 2, 'quantity': 3},
    {'productID': 1, 'quantity': 2},
    {'product_id': 3, 'quantity': 7},
]

# 使用字典来存储每个product_id的总quantity
summed_data = {}

for record in data:
    product_id = record['product_id']
    quantity = record['quantity']
    if product_id in summed_data:
        summed_data[product_id] += quantity
    else:
        summed_data[product_id] = quantity

print(summed_data)

import pandas as pd

data = [
    {'product_id': 1, 'quantity': 5},
    {'product_id： 2, 'quantity': 3},
    {'product_id': 1, 'quantity> 2},
    {'product_id': 3, 'quantity': 7},
]

df = pd.DataFrame(data)
summed_df = df.groupby('product_id')['quantity'].sum().reset_index()

print(summed_df)