Question

我无法弄清楚我在做什么错。我正在查询sqlite表以获取每个学院的最新记录，但结果并不完全准确。下面是源表：

College  Status           Date
"UTAR   "CERTIFIED" "07/30/2018"
"UTA"   "CERTIFIED" "03/19/2018"
"UTD"   "CERTIFIED" "06/08/2018"
"UTEL"  "CERTIFIED" "03/13/2018"
"UTSA"  "CERTIFIED" "02/06/2018"
"UTT"   "CERTIFIED" "03/14/2018"
"UTPB"  "CERTIFIED" "07/23/2018"
"UTRG"  "CERTIFIED" "04/12/2018"
"UTAR"  "CERTIFIED" "05/31/2017"
"UTA"   "CERTIFIED" "03/02/2017"
"UTD"   "CERTIFIED" "04/13/2017"
"UTEL"  "CERTIFIED" "03/10/2017"
"UTSA"  "CERTIFIED" "02/13/2017"
"UTT"   "CERTIFIED" "03/11/2017"
"UTPB"  "CERTIFIED" "03/29/2017"
"UTRG"  "CERTIFIED" "04/12/2017"

这是我的查询：

SELECT *
FROM Status_Table AS S1
WHERE Date = (
                 SELECT MAX(Date)
                 FROM Status_Table AS S2
                 WHERE S1.College = S2.College
                                              );

结果是：

College  Status           Date
"UTAR"  "CERTIFIED" "07/30/2018"
"UTA"   "CERTIFIED" "03/19/2018"
"UTD"   "CERTIFIED" "06/08/2018"
"UTEP"  "CERTIFIED" "03/13/2018"
"UTT"   "CERTIFIED" "03/14/2018"
"UTPB"  "CERTIFIED" "07/23/2018"
"UTRG"  "CERTIFIED" "04/12/2018"
"UTSA"  "CERTIFIED" "02/13/2017"

如果您注意到UTSA，它没有选择最晚的日期02/06/2018。知道我在这里做错了吗？

Answer 1

问题应该与列类型有关。从SQLite文档about date time，

SQLite没有预留存储类来存储日期和/或时间。相反，SQLite内置的日期和时间功能可以将日期和时间存储为TEXT，REAL或INTEGER值：

我不知道创建表时为什么没有警告或错误，但是比较似乎是使用字符串比较而不是日期。该列更改为TEXT，并且在我的sql提琴中应用了日期格式'YYYY-MM-DD'。然后在查询中使用date函数，一切似乎正常。

sql fiddle

Answer 2

您需要按最大日期分组。试试这个-

SELECT *
FROM Status_Table
WHERE Date IN (SELECT MAX(Date)
               FROM Status_Table
               GROUP BY College);

SQLite获取此表的最新记录

2 个答案: