Question

我有一个这样结构的数据库：

int, date, varchar
1, 2021-07-25, aaaa
2, 2021-07-25, aaba
3, 2021-07-25, aabb
4, 2021-07-26, bbbb
5, 2021-07-26, bbba
6, 2021-07-26, bbaa
7, 2021-07-26, babb

我需要为每个日期随机提取一个结果。所以在这个例子中，一个是 07-25 的结果，一个是 07-26 的结果。

样本输出：

<块引用>

啊啊啊
bbbb

Answer 1

你也可以试试

select varchar from table where date='2021-07-25'
order by rand() limit 1;

Answer 2

这里有一个想法，至少，满足简要...

DROP TABLE IF EXISTS ralph97;

CREATE TABLE ralph97
(id INT AUTO_INCREMENT PRIMARY KEY
,date DATE NOT NULL
,my_string CHAR(4) NOT NULL
);

INSERT INTO ralph97 VALUES
(1,'2021-07-25','aaaa'),
(2,'2021-07-25','aaba'),
(3,'2021-07-25','aabb'),
(4,'2021-07-26','bbbb'),
(5,'2021-07-26','bbba'),
(6,'2021-07-26','bbaa'),
(7,'2021-07-26','babb');

...

WITH cte AS
(SELECT *, ROW_NUMBER() OVER (PARTITION BY date ORDER BY RAND()) x FROM ralph97)
SELECT id, date, my_string FROM cte WHERE x = 1;
+----+------------+-----------+
| id | date       | my_string |
+----+------------+-----------+
|  3 | 2021-07-25 | aabb      |
|  6 | 2021-07-26 | bbaa      |
+----+------------+-----------+

WITH cte AS
(SELECT *, ROW_NUMBER() OVER (PARTITION BY date ORDER BY RAND()) x FROM ralph97)
SELECT id, date, my_string FROM cte WHERE x = 1;
+----+------------+-----------+
| id | date       | my_string |
+----+------------+-----------+
|  2 | 2021-07-25 | aaba      |
|  4 | 2021-07-26 | bbbb      |
+----+------------+-----------+

Answer 3

您可以使用 GROUP BY 语句来帮助您实现这一点，查询将如下所示：

SELECT varchar FROM {table-name} GROUP BY date;

从每个日期选择一个随机结果

3 个答案: