fix: optimize

Author: thinkasany

solution/1900-1999/1939.Users That Actively Request Confirmation Messages/README.md

@@ -88,8 +88,7 @@ Result table
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```sql
-SELECT DISTINCT
-    c1.user_id AS user_id
+SELECT DISTINCT user_id
 FROM
     Confirmations AS c1
     JOIN Confirmations AS c2 USING (user_id)

solution/1900-1999/1939.Users That Actively Request Confirmation Messages/README_EN.md

@@ -91,8 +91,7 @@ User 7 requested two messages within 24 hours and 1 second of each other, so we
 ### **SQL**
 
 ```sql
-SELECT DISTINCT
-    c1.user_id AS user_id
+SELECT DISTINCT user_id
 FROM
     Confirmations AS c1
     JOIN Confirmations AS c2 USING (user_id)

solution/1900-1999/1939.Users That Actively Request Confirmation Messages/Solution.sql

@@ -1,5 +1,4 @@
-SELECT DISTINCT
-    c1.user_id AS user_id
+SELECT DISTINCT user_id
 FROM
     Confirmations AS c1
     JOIN Confirmations AS c2 USING (user_id)