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문제
Table: MyNumbers
+-------------+------+
| Column Name | Type |
+-------------+------+
| num | int |
+-------------+------+This table may contain duplicates (In other words, there is no primary key for this table in SQL).
Each row of this table contains an integer.
A single number is a number that appeared only once in the MyNumbers table.
Find the largest single number. If there is no single number, report null.
The result format is in the following example.
https://leetcode.com/problems/biggest-single-number/
예시
Example 1:
Input:
MyNumbers table:
+-----+
| num |
+-----+
| 8 |
| 8 |
| 3 |
| 3 |
| 1 |
| 4 |
| 5 |
| 6 |
+-----+
Output:
+-----+
| num |
+-----+
| 6 |
+-----+Explanation: The single numbers are 1, 4, 5, and 6.
Since 6 is the largest single number, we return it.
Example 2:
Input:
MyNumbers table:
+-----+
| num |
+-----+
| 8 |
| 8 |
| 7 |
| 7 |
| 3 |
| 3 |
| 3 |
+-----+
Output:
+------+
| num |
+------+
| null |
+------+Explanation: There are no single numbers in the input table so we return null.
문제 풀이
SELECT MAX(num) AS num
FROM (SELECT num
FROM mynumbers
GROUP BY num
HAVING COUNT(num) = 1) AS single_num;SELECT num
FROM mynumbers
GROUP BY num
HAVING COUNT(*) = 1
UNION ALL
SELECT null
ORDER BY num DESC
LIMIT 1;SQL을 독학하시는 분들에게 도움이 되길 바라며,
혹 더 좋은 방법이 있거나 오류가 있다면 편하게 말씀 부탁드립니다.
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