SQL 语句中的 Seats Academy 计算

Question

我的分配算法需要基于每个学院名额的剩余名额。

这是我的表格的插图：

tbl学院

    Acad_id name  numberOfSeats
   ------------------------------
    1       A        2
    2       B        2
    3       C        1
    4       D        5
    5       E        3

tbl学生

    stud_Id name   `stud_purcentage` `stud_result`   acad_id
   ----------------------------------------------------------
     1       Alex     100               `Pass`         
     2       Lee      80.5              `Pass`         
     3       Lea      40.3              `Fail`         
     4       Loane    10                `Fail`
     5       john     50                `Pass`         

tblAcademy_selection

   stud_id Acad_id order_preference
   --------------------------------
    1      1          1
    1      3          2
    4      3          1
    4      2          2
    4      4          3

我的算法：

SqlConnection dbcon = new SqlConnection(_conString);
        SqlCommand scmd = new SqlCommand();
        scmd.CommandText = "SELECT stud_Id,stud_fname,stud_purcentage,stud_totalMarks FROM tblStudent where stud_result='Pass' order by stud_purcentage Desc";
        scmd.Connection = dbcon;

        SqlDataAdapter da = new SqlDataAdapter(scmd);
        DataTable dt = new DataTable();
        dbcon.Open();

        da.Fill(dt);
        string[] array = new string[dt.Rows.Count];
        // foreach (DataRow row in dt.Rows)
        for (int a = 0; a < dt.Rows.Count; a++)
        {
        
            array[a] = dt.Rows[a]["stud_Id"].ToString();
            SqlCommand scmd2 = new SqlCommand();
            scmd2.CommandText = "select acad_Id,stud_Id from(SELECT tas.*, DENSE_RANK() OVER (PARTITION BY stud_id ORDER BY order_preference) AS row_id FROM tblAcademy ta JOIN tblAcademy_Selection tas ON ta.acad_Id = tas.acad_Id WHERE ta.numberOfSeats > 0 and stud_Id IN('" + array[a] + "')) DTL WHERE row_id = 1";
            scmd2.Connection= dbcon;
            SqlDataAdapter da2 = new SqlDataAdapter(scmd2);
            DataTable dt2 = new DataTable();
            da2.Fill(dt2);
            string[] array2 = new string[dt2.Rows.Count];
            string[] array3 = new string[dt2.Rows.Count];
            for (int a2 = 0; a2 < dt2.Rows.Count; a2++)
            {
               String acad_Id = dt2.Rows[a2]["acad_Id"].ToString();
                array2[a2] = dt2.Rows[a2]["stud_id"].ToString();
                //string[,] array3 = new string[array2[a2],];
                SqlCommand scmd3 = new SqlCommand();
                scmd3.CommandText = "update tblStudent set acad_id='" + acad_Id + "' where stud_Id='" + array2[a2] + "'";
                scmd3.Connection = dbcon;
                scmd3.ExecuteNonQuery();
                //ListBox1.Items.Add(array5);

            }
          
        }
        getStudent();

在 scmd2 我的 sql 正在寻找一个静态列 numberOfSeats WHERE ta.numberOfSeats > 0（学院配额），这不是我要寻找的。​​p>

我需要的是 where 条件基于计算 tblStudent 中每个 acadID 的总行数 - tblAcademy 中每个 acadID 的 numberOfSeat（学院配额）。

这里是获取剩余席位sql代码的代码：

SELECT distinct ta.acad_Id, numberOfSeats - Count(ts.acad_id) OVER (
    PARTITION BY ta.acad_Id
) as remainingSeat
FROM tblAcademy ta,
     tblStudent ts
where ta.acad_Id = ts.acad_Id or ts.acad_Id is null

我很难将smcd2 command text 的sql 代码定位到remainingSeat 别名而不是ta.numberOfSeats

Answer 1

看来你想多了。要查找剩余座位数，您只需要一个相关的子查询

SELECT
  ta.acad_Id,
  ta.numberOfSeats - ts.cn as remainingSeat
FROM tblAcademy ta
OUTER APPLY (
    SELECT COUNT(*) AS cn
    FROM tblStudent ts
    WHERE ta.acad_Id = ts.acad_Id
) ts
WHERE ta.numberOfSeats - ts.total > 0;

-- or as a pre-grouped joined 

SELECT
  ta.acad_Id,
  ta.numberOfSeats - ts.cn as remainingSeat
FROM tblAcademy ta
LEFT JOIN (
    SELECT
      ts.acad_Id,
      COUNT(*) AS cn
    FROM tblStudent ts
) ts ON ta.acad_Id = ts.acad_Id
WHERE ta.numberOfSeats - ts.cn;

目前尚不清楚您要对scmd2 中的查询执行什么操作

旁注：

• 始终参数化您的查询，不要向其中注入数据。
• 不要使用旧式 , 交叉连接，它们在 30 年前已被弃用。