Merge pull request #19 from iamAntimPal/Branch-1

Create 180. Consecutive Numbers.sql

Author: iamAntimPal

LeetCode SQL 50 Solution/180. Consecutive Numbers.sql

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+180. Consecutive Numbers
+"""
+# Write your MySQL query statement below
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| id          | int     |
+| num         | varchar |
++-------------+---------+
+In SQL, id is the primary key for this table.
+id is an autoincrement column starting from 1.
+ 
+
+Find all numbers that appear at least three times consecutively.
+
+Return the result table in any order.
+
+The result format is in the following example.
+
+ 
+
+Example 1:
+
+Input: 
+Logs table:
++----+-----+
+| id | num |
++----+-----+
+| 1  | 1   |
+| 2  | 1   |
+| 3  | 1   |
+| 4  | 2   |
+| 5  | 1   |
+| 6  | 2   |
+| 7  | 2   |
++----+-----+
+Output: 
++-----------------+
+| ConsecutiveNums |
++-----------------+
+| 1               |
++-----------------+
+
+"""
+Explanation: 1 is the only number that appears consecutively for at least three times.
+
+# Write your MySQL query statement below
+with consecutive_runs as (
+    select id, num, lead(num, 1) over (order by id) as lead_num, lag(num, 1) over (order by id) as lag_num
+    from Logs
+)
+select distinct num as ConsecutiveNums
+from consecutive_runs 
+where num = lead_num and num = lag_num
+
+"""
+Explanation
+ Common Table Expression (CTE): consecutive_runs
+sql
+Copy
+Edit
+with consecutive_runs as (
+    select 
+        id, 
+        num, 
+        lead(num, 1) over (order by id) as lead_num, 
+        lag(num, 1) over (order by id) as lag_num
+    from Logs
+)
+Purpose of the CTE:
+This part creates a temporary result set named consecutive_runs that enriches each row from the Logs table with two extra columns:
+
+lead_num: The value of the num column in the next row (based on the id order).
+lag_num: The value of the num column in the previous row (based on the id order).
+Window Functions:
+
+lead(num, 1) over (order by id):
+This function returns the value of num from the row immediately following the current one when sorted by id.
+lag(num, 1) over (order by id):
+This function returns the value of num from the row immediately preceding the current one when sorted by id.
+This setup allows us to compare each row with its immediate neighbors.
+
+2. Final SELECT Query
+sql
+Copy
+Edit
+select distinct num as ConsecutiveNums
+from consecutive_runs 
+where num = lead_num and num = lag_num
+Filtering Condition:
+The WHERE clause checks if the current row's num value is equal to both its next (lead_num) and previous (lag_num) values:
+
+num = lead_num
+num = lag_num
+This ensures that the number appears consecutively (at least three times in a row).
+
+DISTINCT Keyword:
+The distinct keyword makes sure that each number is listed only once in the final output, even if it occurs in multiple consecutive sequences.
+
+Result Column Alias:
+The output column is renamed to ConsecutiveNums for clarity.
+
+Summary
+CTE Usage:
+The query first computes additional columns using window functions (lead and lag) to look at neighboring rows.
+
+Consecutive Check:
+It then filters out rows where the current value is the same as both the previous and next value, meaning there are at least three consecutive occurrences of that number.
+
+Final Output:
+The final result is a list of distinct numbers that appear consecutively in the Logs table.
+"""