android - sqLite - 使用 CAST 修改列中的 GROUP BY

Question

我正在使用 Android SQLite（使用 Galaxy s2 进行测试）我无法解决这个问题

我有一个这样的数据库：

COORDINATES
id latitude   longitude
1  37.996163  -116.644592
2  37.996163  -116.644592
3  37.957507  -116.67467
4  36.370157  -91.156311

我运行查询：

select CAST((latitude*10) AS UNSIGNED) AS lat, CAST((longitude*10) AS UNSIGNED) AS lon from coordinates group by lat,lon

我预计：

lat  lon
379  -1166
363  -911

相反，我得到：

lat  lon
379  -1166
379  -1166
363  -911

对未由 CAST 修改的值执行“分组依据”我做错了什么？mysql 上的相同查询完美运行。

谢谢

Answer 1

试试这个，我不确定这是否可行，但我知道 select 子句中的更改在 where、group 中不起作用……所以试试这个

select CAST((latitude*10) AS UNSIGNED) AS lat, CAST((longitude*10) AS UNSIGNED) AS lon
from coordinates 
group by CAST((latitude*10) AS UNSIGNED), CAST((longitude*10) AS UNSIGNED)

Answer 2

sqlite 没有UNSIGNED数据类型，并且对其进行强制转换并没有真正做任何事情。这些值是浮点数，直到您调用例如Cursor getInt()将它们转换为整数。

改为例如INTEGER：

sqlite> create table coordinates(id integer primary key, latitude, longitude);
sqlite> insert into coordinates values(1,37.996163,-116.644592),(2,37.996163,-116.644592),(3,37.957507,-116.67467),(4,36.370157,-91.156311);
sqlite> .head on
sqlite> select CAST((latitude*10) AS UNSIGNED) AS lat, CAST((longitude*10) AS UNSIGNED) AS lon from coordinates group by lat,lon;
lat|lon
363.70157|-911.56311
379.57507|-1166.7467
379.96163|-1166.44592
sqlite> select CAST((latitude*10) AS INTEGER) AS lat, CAST((longitude*10) AS INTEGER) AS lon from coordinates group by lat,lon;
lat|lon
363|-911
379|-1166
sqlite>