Question

1613. Find the Missing IDs

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Description

Table: Customers

+---------------+---------+
| Column Name   | Type  |
+---------------+---------+
| customer_id   | int   |
| customer_name | varchar |
+---------------+---------+
customer_id is the column with unique values for this table.
Each row of this table contains the name and the id customer.

 

Write a solution to find the missing customer IDs. The missing IDs are ones that are not in the Customers table but are in the range between 1 and the maximum customer_id present in the table.

Notice that the maximum customer_id will not exceed 100.

Return the result table ordered by ids in ascending order.

The result format is in the following example.

 

Example 1:

Input: 
Customers table:
+-------------+---------------+
| customer_id | customer_name |
+-------------+---------------+
| 1       | Alice     |
| 4       | Bob       |
| 5       | Charlie     |
+-------------+---------------+
Output: 
+-----+
| ids |
+-----+
| 2   |
| 3   |
+-----+
Explanation: 
The maximum customer_id present in the table is 5, so in the range [1,5], IDs 2 and 3 are missing from the table.

Solutions

Solution 1

# Write your MySQL query statement below
WITH RECURSIVE
  t AS (
    SELECT
      1 AS n
    UNION ALL
    SELECT
      n + 1
    FROM t
    WHERE n < 100
  )
SELECT
  n AS ids
FROM t
WHERE
  n < (
    SELECT
      MAX(customer_id)
    FROM Customers
  )
  AND n NOT IN (
    SELECT
      customer_id
    FROM Customers
  );