Find_Customer_Referee.sql

PROBLEM:

584.Find Customer Referee

Table: Customer

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| name        | varchar |
| referee_id  | int     |
+-------------+---------+
id is the primary key column for this table.
Each row of this table indicates the id of a customer, their name, and the id of the customer who referred them.
 

Write an SQL query to report the names of the customer that are not referred by the customer with id = 2.

Return the result table in any order.

The query result format is in the following example.

 

Example 1:

Input: 
Customer table:
+----+------+------------+
| id | name | referee_id |
+----+------+------------+
| 1  | Will | null       |
| 2  | Jane | null       |
| 3  | Alex | 2          |
| 4  | Bill | null       |
| 5  | Zack | 1          |
| 6  | Mark | 2          |
+----+------+------------+
Output: 
+------+
| name |
+------+
| Will |
| Jane |
| Bill |
| Zack |
+------+



Solution:

# Write your MySQL query statement below
#Here's my solution
#Parul Sharma


#1.
SELECT
name
FROM
customer
WHERE
referee_id <> 2 or referee_id IS NULL;

#2.
SELECT name
FROM customer
WHERE COALESCE(referee_id,0) <> 2;

#here COALESCE is used to replace NULL values with zero before checking whether it is equal to 2 or not.