feat: update sql solution to lc problem: No.2020 (#1901)

Author: thinkasany

solution/2000-2099/2020.Number of Accounts That Did Not Stream/README.md

@@ -90,10 +90,10 @@ Streams table:
 
 ```sql
 # Write your MySQL query statement below
-SELECT COUNT(DISTINCT sub.account_id) AS accounts_count
+SELECT COUNT(sub.account_id) AS accounts_count
 FROM
     Subscriptions AS sub
-    LEFT JOIN Streams AS ss ON sub.account_id = ss.account_id
+    LEFT JOIN Streams USING (account_id)
 WHERE
     YEAR(start_date) <= 2021
     AND YEAR(end_date) >= 2021

solution/2000-2099/2020.Number of Accounts That Did Not Stream/README_EN.md

@@ -87,10 +87,10 @@ User 11 did not subscribe in 2021.
 
 ```sql
 # Write your MySQL query statement below
-SELECT COUNT(DISTINCT sub.account_id) AS accounts_count
+SELECT COUNT(sub.account_id) AS accounts_count
 FROM
     Subscriptions AS sub
-    LEFT JOIN Streams AS ss ON sub.account_id = ss.account_id
+    LEFT JOIN Streams USING (account_id)
 WHERE
     YEAR(start_date) <= 2021
     AND YEAR(end_date) >= 2021

solution/2000-2099/2020.Number of Accounts That Did Not Stream/Solution.sql

@@ -1,8 +1,8 @@
 # Write your MySQL query statement below
-SELECT COUNT(DISTINCT sub.account_id) AS accounts_count
+SELECT COUNT(sub.account_id) AS accounts_count
 FROM
     Subscriptions AS sub
-    LEFT JOIN Streams AS ss ON sub.account_id = ss.account_id
+    LEFT JOIN Streams USING (account_id)
 WHERE
     YEAR(start_date) <= 2021
     AND YEAR(end_date) >= 2021