Question

我有这种表：

Problem    UserID  Grade
Probleme1  ID1     33
Probleme1  ID2     100
Probleme1  ID4     57
Probleme1  ID6     57
Probleme1  ID78    24
Probleme1  ID5     24
Probleme2  ID1     37
Probleme2  ID12    88
Probleme2  ID6846  100
Probleme2  ID2     2

我想要实现的目标是创建一个包含以下内容的表：

对于每个问题，整个等级范围（从0到100，即使没有人有这个问题的87，我希望它显示为0值）
每个年级（每个问题），获得此成绩的人数。

所以我试着像这样做：

DROP TABLE IF EXISTS Problem_Grades_Point;
CREATE TABLE Problem_Grades_Point (
  Platform VARCHAR(20),
  AnalyticsDomain VARCHAR(255),
  ShortTitle VARCHAR(255),
  Problem VARCHAR(255),
  Grade0 INT,
  Grade10 INT,
  Grade20 INT,
  INDEX (Problem)
) ENGINE=INNODB CHARACTER SET utf8 COLLATE utf8_bin;

INSERT INTO Problem_Grades_Point
SELECT
  Platform,
  AnalyticsDomain,
  ShortTitle,
  Problem,
  COUNT(Problem) AS Grade0,
  0 as Grade10,
  0 as Grade20
FROM First_Attempt_Problem_Grades
WHERE First_Grade = 0
GROUP BY Problem

UNION ALL 

SELECT
  Platform,
  AnalyticsDomain,
  ShortTitle,
  Problem,
  0 as Grade0,
  COUNT(t.Problem) AS Grade10,
  0 as Grade20
  FROM First_Attempt_Problem_Grades t
WHERE First_Grade = 10
GROUP BY Problem

UNION ALL 

SELECT
  Platform,
  AnalyticsDomain,
  ShortTitle,
  Problem,
  0 as Grade0,
  0 as Grade10,
  COUNT(Problem) AS Grade20
  FROM First_Attempt_Problem_Grades
WHERE First_Grade = 20
GROUP BY Problem

当然，它并不包含我想要的一切，当然，它也不起作用。它仅显示0级的结果。所有其他成绩均为空，如下所示：

The Mysql's query result

我该如何做这个SOV社区？：）

Answer 1

首先，您需要一个成绩列表。因此，您创建一个数字表，其成绩从1到100，并将其命名为SELECT P.Problem, G.Grade, COUNT(Y.UserID) FROM ( SELECT DISTINCT Problem FROM YourTable) as P -- if you have a table `Problems` you can use it instead CROSS JOIN Grades as G LEFT JOIN YourTable Y ON P.Problem = Y.Problem AND G.Grade = Y.Grade GROUP BY P.Problem, G.Grade

How do I get a list of numbers in MySQL?

现在你做：

public class StudentController : ApiController
{
    [HttpDelete]
    [Route("student/DeleteStudent/{id}")]

    public IHttpActionResult DeleteStudent(string id)
    {
        using (var sd = new SchoolDBEntities())
        {
            var student = sd.Students
                .Where(s => s.StudentID == id)
                .FirstOrDefault();

            sd.Entry(student).State = System.Data.Entity.EntityState.Deleted;
            sd.SaveChanges();
        }
        if (id == null)
        return BadRequest("Not a valid student id");

        return Ok();
    }
}

按不同等级分组，了解他们的等级

1 个答案: