Number of accounts that did not stream

# Table: Subscriptions
# 
# +-------------+------+
# | Column Name | Type |
# +-------------+------+
# | account_id  | int  |
# | start_date  | date |
# | end_date    | date |
# +-------------+------+
# account_id is the primary key column for this table.
# Each row of this table indicates the start and end dates of an account's subscription.
# Note that always start_date < end_date.
# 
#  
# 
# Table: Streams
# 
# +-------------+------+
# | Column Name | Type |
# +-------------+------+
# | session_id  | int  |
# | account_id  | int  |
# | stream_date | date |
# +-------------+------+
# session_id is the primary key column for this table.
# account_id is a foreign key from the Subscriptions table.
# Each row of this table contains information about the account and the date associated with a stream session.
# 
#  
# 
# Write an SQL query to report the number of accounts that bought a subscription in 2021 but did not have any stream session.
# 
# The query result format is in the following example.
#
# Example 1:
# Input:
# Subscriptions table:
# +------------+------------+------------+
# | account_id | start_date | end_date   |
# +------------+------------+------------+
# | 9          | 2020-02-18 | 2021-10-30 |
# | 3          | 2021-09-21 | 2021-11-13 |
# | 11         | 2020-02-28 | 2020-08-18 |
# | 13         | 2021-04-20 | 2021-09-22 |
# | 4          | 2020-10-26 | 2021-05-08 |
# | 5          | 2020-09-11 | 2021-01-17 |
# +------------+------------+------------+
# Streams table:
# +------------+------------+-------------+
# | session_id | account_id | stream_date |
# +------------+------------+-------------+
# | 14         | 9          | 2020-05-16  |
# | 16         | 3          | 2021-10-27  |
# | 18         | 11         | 2020-04-29  |
# | 17         | 13         | 2021-08-08  |
# | 19         | 4          | 2020-12-31  |
# | 13         | 5          | 2021-01-05  |
# +------------+------------+-------------+
# Output:
# +----------------+
# | accounts_count |
# +----------------+
# | 2              |
# +----------------+
# Explanation: Users 4 and 9 did not stream in 2021.
# User 11 did not subscribe in 2021.

import pandas as pd

def find_target_accounts(subscriptions: pd.DataFrame, streams: pd.DataFrame) -> pd.DataFrame:
  # Accounts that bought subscription in 2021 (subscription period overlaps with 2021)
  subs_2021 = subscriptions[
    (subscriptions['start_date'].dt.year <= 2021) & (subscriptions['end_date'].dt.year >= 2021)
  ]
  # Accounts that streamed in 2021
  streams_2021 = streams[streams['stream_date'].dt.year == 2021]['account_id'].unique()
  # Filter accounts that did not stream in 2021
  no_stream = subs_2021[~subs_2021['account_id'].isin(streams_2021)]
  result = pd.DataFrame({'accounts_count': [no_stream['account_id'].nunique()]})
  return result