Find Customer Referee | LeetCode | MSSQL

The Problem

The challenge involves a table, Customer.

Customer table:

The goal is to write an SQL query to report the names of the customers that were not referred by the customer with id = 2.

Explanation

Here's an example for better understanding:

Input:

Customer table:

Output:

Will, Jane, Bill, and Zack were not referred by the customer with id = 2.

The Solution

We'll explore two SQL solutions that solve this problem with subtle differences. We'll discuss their differences, strengths, weaknesses, and structures.

Source Code 1

The first solution selects customers whose referee_id is not 2 or is null.

SELECT name
FROM Customer
WHERE
  referee_id != 2
  OR
  referee_id IS NULL

This solution has a runtime of 740ms, outperforming 91.47% of other submissions.

Source Code 2

The second solution closely resembles the first. The only difference is the order of conditions in the WHERE clause. It first checks for null referee_ids before checking for referee_ids not equal to 2.

SELECT name
FROM Customer
WHERE
  referee_id IS NULL
  OR
  referee_id != 2

The runtime for this solution is 741ms, beating 91.35% of other submissions.

Conclusion

Both solutions yield the desired outcome, but the first solution performs marginally better. Consequently, the ranking of solutions based on overall performance, from best to worst, is as follows: Source Code 1 > Source Code 2.

Your choice should depend on your specific requirements and performance expectations.

You can find the original problem at LeetCode.

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