假设我有3列，ID，firstcolumn，secondcolumn。
我需要根据secondcolumn的值检索firstcolumn的最大id。此返回的id必须是firstcolumn的最大id，但仍必须小于或等于每个记录的第二列的值。
数据集：
+----+-------------+--------------+
| ID | firstcolumn | secondcolumn |
+----+-------------+--------------+
| 1 | 32 | 32 |
| 1 | 32 | 35 |
| 1 | 32 | 38 |
| 1 | 34 | 32 |
| 1 | 34 | 35 |
| 1 | 34 | 38 |
| 1 | 39 | 32 |
| 1 | 39 | 35 |
| 1 | 39 | 38 |
| 2 | 12 | 12 |
| 2 | 12 | 17 |
| 2 | 18 | 12 |
| 2 | 18 | 17 |
+----+-------------+--------------+
生成的数据集
+----+-------------+--------------+--------------+
| ID | firstcolumn | secondcolumn | resultcolumn |
+----+-------------+--------------+--------------+
| 1 | 32 | 32 | 32 |
| 1 | 32 | 35 | 34 |
| 1 | 32 | 38 | 34 |
| 1 | 34 | 32 | 32 |
| 1 | 34 | 35 | 34 |
| 1 | 34 | 38 | 34 |
| 1 | 39 | 32 | 32 |
| 1 | 39 | 35 | 34 |
| 1 | 39 | 38 | 34 |
| 2 | 12 | 12 | 12 |
| 2 | 12 | 17 | 12 |
| 2 | 18 | 12 | 12 |
| 2 | 18 | 17 | 12 |
+----+-------------+--------------+--------------+
非常感谢任何帮助！
答案 0 :(得分：0)
您的解释转换为相关标量子查询：
select *,
( select max(firstcolumn) -- maximum id of firstcolumn
from tab as t2
where t1.id = t2.id
and t2.firstcolumn <= t1.secondcolumn -- less than or equal to secondcolumn
)
from tab as t1