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.