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LeetCode SQL 50 - 584. Find Customer Feferee
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 1 :
# Write your MySQL query statement below
SELECT name
FROM Customer
WHERE referee_id <> '2' OR referee_id IS NULL
Solution 2 :
# Write your MySQL query statement below
SELECT name
FROM Customer
WHERE COALESCE(referee_id, '') <> '2'
Solution 3 :
# Write your MySQL query statement below
select name
from Customer
where IFNULL(referee_id, '') <> '2'COALESCE 함수 사용하기
SELECT COALESCE(a_section, b_section, c_section)
FROM 테이블명
- a_section이 NULL인 경우 b_section을 반환
- b_section도 NULL 인 경우 c_section을 반환
- 인자가 3개
IFNULL 함수 사용하기
SELECT IFNULL(a_section, b_section)
FROM 테이블명- a_section이 NULL인 경우 b_section을 반환
- 인자가 2개
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