Question

我有数据库表P，看起来像这样：

date        wellID  rate
01/01/1988  well01  300
01/02/1988  well01  301
01/03/1988  well01  310
........
01/04/1988  well02  500
01/05/1988  well02  490
01/06/1988  well02  495
........
01/04/1988  well03  700
01/05/1988  well03  750
01/06/1988  well03  700
........   
01/07/1989  well04  400
01/08/1989  well04  350
01/09/1989  well04  340
........

我想提取每口井的初始速率，即每口井最早记录的日期以及相关的速率。我期待这样的事情：

date        wellID  oil
01/01/1988  well01  300
01/04/1988  well02  500
01/04/1988  well03  700
01/07/1989  well04  400

我正在尝试使用以下SQL查询从Access中提取此数据

SELECT p.date, p.wellID, p.oil
FROM p 
LEFT JOIN
(
   SELECT wellID, min(date) AS MinDate
   FROM p
) AS a 
ON p.wellID = a.wellID
WHERE p.date = a.MinDate;

但Access提供此消息“您试图执行不包含指定表达式'WellId'作为聚合函数的一部分的查询”。我担心这超出了我对SQL的有限知识，所以所有人都非常感谢

谢谢！

Answer 1

添加group by，您可能希望此案例INNER JOIN

INNER JOIN
(
   SELECT wellID, min(date) AS MinDate
   FROM p
   GROUP BY wellID
) AS a

Answer 2

您在内部聚合查询中遗漏了一个group by子句。

试试这个：

SELECT p.date, p.wellID, p.oil
FROM p 
LEFT JOIN
(
   SELECT wellID, min(date) AS MinDate
   FROM p
   GROUP BY wellID
) AS a 
ON p.wellID = a.wellID
WHERE p.date = a.MinDate;

使用子查询来混淆JOIN

2 个答案: