feat: add sql solution to lc problem: No.0550

No.0550.Game Play Analysis IV

Author: yanglbme

solution/0500-0599/0550.Game Play Analysis IV/README.md

@@ -56,7 +56,17 @@ Result table:
 ### **SQL**
 
 ```sql
-
+# Write your MySQL query statement below
+SELECT  round( AVG( b.event_date IS NOT NULL ),2 ) fraction
+FROM
+(
+	SELECT  player_id
+	       ,MIN( event_date ) AS event_date
+	FROM activity
+	GROUP BY  player_id
+) a
+LEFT JOIN activity b
+ON a.player_id = b.player_id AND DATEDIFF( a.event_date, b.event_date ) = -1
 ```
 
 <!-- tabs:end -->

solution/0500-0599/0550.Game Play Analysis IV/README_EN.md

@@ -58,7 +58,17 @@ Only the player with id 1 logged back in after the first day he had logged in so
 ### **SQL**
 
 ```sql
-
+# Write your MySQL query statement below
+SELECT  round( AVG( b.event_date IS NOT NULL ),2 ) fraction
+FROM
+(
+	SELECT  player_id
+	       ,MIN( event_date ) AS event_date
+	FROM activity
+	GROUP BY  player_id
+) a
+LEFT JOIN activity b
+ON a.player_id = b.player_id AND DATEDIFF( a.event_date, b.event_date ) = -1
 ```
 
 <!-- tabs:end -->

solution/0500-0599/0550.Game Play Analysis IV/Solution.sql

@@ -0,0 +1,11 @@
+# Write your MySQL query statement below
+SELECT  round( AVG( b.event_date IS NOT NULL ),2 ) fraction
+FROM
+(
+	SELECT  player_id
+	       ,MIN( event_date ) AS event_date
+	FROM activity
+	GROUP BY  player_id
+) a
+LEFT JOIN activity b
+ON a.player_id = b.player_id AND DATEDIFF( a.event_date, b.event_date ) = -1