我希望按一列分组,获取第二列的最小值和最大值,并且(这是棘手的部分!)从第三列获取值,其中第二列在组中具有其最小值。 / p>
示例:
MyTable的:
ID TS GRP
==================
1 20 A
2 20 B
3 10 A
4 30 A
5 10 B
6 40 A
期望的结果(ID应该是TS最小的记录中的值):
ID MIN_TS MAX_TS GRP
============================
3 10 40 A
5 10 20 B
通常,分组查询非常简单:
SELECT <???> AS ID, MIN(TS) AS MIN_TS, MAX(TS) AS MAX_TS, GRP
FROM MyTable
GROUP BY GRP
但ID部分怎么样?它不会以这种方式进行分组,对吧?但为什么?什么是最好的解决方法?
答案 0 :(得分:2)
在子查询中进行聚合,然后在另一个子查询中查找每个组的ID:
SELECT
(SELECT TOP(1) id FROM MyTable WHERE grp = agg.grp ORDER BY ts DESC) AS id,
min_ts, max_ts, grp
FROM (SELECT min(ts) AS min_ts, max(ts) AS max_ts, grp
FROM MyTable
GROUP BY grp) agg
或使用窗口功能:
SELECT id, min_ts, max_ts, grp
FROM (SELECT
id,
min(ts) OVER (PARTITION BY grp) min_ts,
max(ts) OVER (PARTITION BY grp) max_ts,
grp,
row_number OVER (PARTITION BY grp ORDER BY ts) rn
FROM MyTable)
WHERE rn = 1;
此查询使用窗口函数计算每个组的min_ts
和max_ts
,然后过滤为仅包含每个组的第一行(按ts
排序)。