Android Sqlite 计算：如何分别总结两列并将一列总和除以另一列总和

Question

伙计们，根据我的时区，我应该说早上好

我正在开发一个 android 项目，该项目将组合或连接两个表并按 id 显示，它工作了我现在想知道如何分别总结两列并将一列总和除以同一函数的另一列总和

到目前为止我的进步

  public List<Courses> getListCourses(int id) {
    Courses courses = null;
    List<Courses> coursesList = new ArrayList<>();
    openDatabase();

    Cursor cursor = mDatabase.rawQuery("SELECT * FROM COURSES C INNER JOIN SEMESTER S ON S.semester_id=C.semester_id AND S.LEVEL_ID = C.LEVEL_ID AND S.LEVEL_CODE = C.LEVEL_CODE WHERE C.semester_id =  ?", new String[]{String.valueOf(id)});

    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
        courses = new Courses(cursor.getInt(0), cursor.getInt(1), cursor.getString(2), cursor.getInt(3), cursor.getInt(4), cursor.getString(5), cursor.getInt(6), cursor.getString(7), cursor.getInt(8));
        coursesList.add(courses);
        cursor.moveToNext();
    }
    cursor.close();
    closeDatabase();
    return coursesList;
}

这是两张表

学期表

   Id  |   semester_id    |   semester_code    |   level
   -------------------------------------------------
   1   |   1              |   1st Semester     |   100       
   2   |   2              |   2nd Semester     |   100        
   3   |   3              |   1st Semester     |   100       
   4   |   4              |   2nd Semester     |   100        
   5   |   5              |   1st Semester     |   100        

课程表

 Id  |Se_id| grade |  level |  semester     |  credit_unit  |  gp_unit
 ----------------------------------------------------------------------
 62  |  1  |  A   |  100   |  1st Semester  |  2           |  5
 63  |  1  |  B   |  100   |  1st Semester  |  2           |  4
 64  |  2  |  C   |  100   |  2nd Semester  |  2           |  3
 65  |  2  |  A   |  100   |  2nd Semester  |  2           |  5
 66  |  1  |  C   |  100   |  1st Semester  |  3           |  2

我想总结 CREDIT_UNIT 列并总结 GP_UNIT 列并将 GP_UNIT 总结除以 CREDIT_UNIT 总结我卡住了不知道如何添加它

 Cursor cursor = mDatabase.rawQuery("SELECT * FROM COURSES C INNER JOIN SEMESTER S ON S.semester_id=C.semester_id AND S.LEVEL_ID = C.LEVEL_ID AND S.LEVEL_CODE = C.LEVEL_CODE WHERE C.semester_id =  ?", new String[]{String.valueOf(id)});

Answer 1

你可以使用求和法，然后将其存储在变量中进行划分

int creditunit,gpunit;
cursor = db.rawQuery("select sum(credit_unit) from FROM COURSES C INNER JOIN SEMESTER S ON S.semester_id=C.semester_id AND S.LEVEL_ID = C.LEVEL_ID AND S.LEVEL_CODE = C.LEVEL_CODE WHERE C.semester_id =  ? ;", new String[]{String.valueOf(id)});
if(cursor.moveToFirst())
    creditunit =cursor.getInt(0);
else
    creditunit = -1;
cursor.close();

cursor = db.rawQuery("select sum(gp_unit) FROM COURSES C INNER JOIN SEMESTER S ON S.semester_id=C.semester_id AND S.LEVEL_ID = C.LEVEL_ID AND S.LEVEL_CODE = C.LEVEL_CODE WHERE C.semester_id =  ? ;", new String[]{String.valueOf(id)});
if(cursor.moveToFirst())
    gpunit =cursor.getInt(0);
else
    gpunit = -1;
cursor.close();
//perform division
double sol= creditunit/gpunit;

编辑：查询是 ,

 cursor = db.rawQuery("select sum(credit_unit),sum(gp_unit) from FROM COURSES C INNER JOIN SEMESTER S ON S.semester_id=C.semester_id AND S.LEVEL_ID = C.LEVEL_ID AND S.LEVEL_CODE = C.LEVEL_CODE WHERE C.semester_id =  ? ;", new String[]{String.valueOf(id)});

更新

要在你的活动中访问适配器类的代码，

将您的任务作为活动中的方法，

public void getsolution(double sol)
{
    //code for displaying sol in textview
}

然后在你的适配器类中，

1.在构造函数中传递活动引用

public adapter(YourActivity activity)

2.执行完你的sql代码，调用activity方法

 activity.getsolution(sol);