Create biggest-window-between-visits.sql

Author: kamyu104

MySQL/biggest-window-between-visits.sql

@@ -0,0 +1,21 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT
+    user_id,
+    MAX(DATEDIFF(visit_date_after, visit_date)) AS biggest_window
+FROM (
+    SELECT
+        user_id,
+        visit_date,
+        IFNULL(
+            LEAD(visit_date, 1) OVER (
+                PARTITION BY user_id
+                ORDER BY visit_date
+            ),
+            '2021-1-1'
+        ) AS visit_date_after
+    FROM UserVisits
+) tmp
+GROUP BY 1
+ORDER BY NULL;