Table Joins with pd.merge() and Indicator Auditing in Pandas

Question

Given `users_df` and `orders_df`, perform a left join on `user_id`. Use `indicator=True` to find users who have never placed an order.

Accepted Answer

Optimal Solution:
import pandas as pd

# Left join with indicator column
merged = pd.merge(users_df, orders_df, on='user_id', how='left', indicator=True)

# Unmatched records have _merge == 'left_only'
unplaced_users = merged[merged['_merge'] == 'left_only']

Technical Explanation:
`indicator=True` adds a categorical column `_merge` containing `'both'`, `'left_only'`, or `'right_only'`, simplifying anti-join filtering.

user_id	name	order_id
1	Aarav	901
2	Bhavna	NULL