您想使用 GROUP_CONCAT 和 SUBSTRING_INDEX :

SUBSTRING_INDEX( GROUP_CONCAT(CAST(open AS CHAR) ORDER BY datetime), ',', 1 ) AS open
SUBSTRING_INDEX( GROUP_CONCAT(CAST(close AS CHAR) ORDER BY datetime DESC), ',', 1 ) AS close 

这避免了昂贵的子查询，而且我发现它对于这个特定问题通常更有效.

This avoids expensive sub queries and I find it generally more efficient for this particular problem.

查看这两个函数的手册页以了解它们的参数，或访问这篇文章，其中包含如何执行的示例 MySQL 中的时间帧转换 以获取更多解释.

Check out the manual pages for both functions to understand their arguments, or visit this article which includes an example of how to do timeframe conversion in MySQL for more explanations.