feat: add sql solution to lc problem: No.0602 (doocs#779)

No.0602.Friend Requests II: Who Has the Most Friends

Author: Dhoni77

solution/0600-0699/0602.Friend Requests II Who Has the Most Friends/README.md

@@ -71,7 +71,19 @@ RequestAccepted 表：
 ### **SQL**
 
 ```sql
-
+SELECT 
+    ids AS id, COUNT(*) num
+FROM
+    (SELECT 
+        requester_id AS ids
+    FROM
+        RequestAccepted UNION ALL SELECT 
+        accepter_id
+    FROM
+        RequestAccepted) t
+GROUP BY ids
+ORDER BY num DESC
+LIMIT 1;
 ```
 
 <!-- tabs:end -->

solution/0600-0699/0602.Friend Requests II Who Has the Most Friends/README_EN.md

@@ -60,7 +60,19 @@ The person with id 3 is a friend of people 1, 2, and 4, so he has three friends
 ### **SQL**
 
 ```sql
-
+SELECT 
+    ids AS id, COUNT(*) num
+FROM
+    (SELECT 
+        requester_id AS ids
+    FROM
+        RequestAccepted UNION ALL SELECT 
+        accepter_id
+    FROM
+        RequestAccepted) t
+GROUP BY ids
+ORDER BY num DESC
+LIMIT 1;
 ```
 
 <!-- tabs:end -->

solution/0600-0699/0602.Friend Requests II Who Has the Most Friends/Solution.sql

@@ -0,0 +1,14 @@
+SELECT 
+    ids AS id, COUNT(*) num
+FROM
+    (SELECT 
+        requester_id AS ids
+    FROM
+        RequestAccepted UNION ALL SELECT 
+        accepter_id
+    FROM
+        RequestAccepted) t
+GROUP BY ids
+ORDER BY num DESC
+LIMIT 1;
+