Retrieve id with condition - asp.net

Question

I am trying to allocate academy for student with only one click. This allocation need to have condition before allocating a specific academy to the student.
Here are my database tables:
tblAcademy
Acad_id name seat_available
------------------------------
1 A 2
2 B 2
3 C 1
4 D 5
5 E 3
tblStudent
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
Acad_id is foreign key of tblAcademy. The acad_id can remain null if the condition is not respected a student may do not have academy.
In the tblAcademy selection it shows that a student can select many academy but only one has to be allocate to them.
The allocation must be based on the seat available by the academy, on those who pass and allocate those from best percentage to the worst.
Till now I have been able to retrieve from the best to worst student and those who passed. I have then join those student id to the tblAcademy_selection.
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++)
{
// studID = row["stud_Id"].ToString();
array[a] = dt.Rows[a]["stud_Id"].ToString();
SqlCommand scmd2 = new SqlCommand();
scmd2.CommandText = "SELECT * FROM tblAcademy ta JOIN tblAcademy_Selection tas ON ta.acad_Id = tas.acad_Id WHERE stud_Id IN ('" + array[a] + "')";
scmd2.Connection = dbcon;
SqlDataAdapter da2 = new SqlDataAdapter(scmd2);
DataTable dt2 = new DataTable();
da2.Fill(dt2);
string[] array2 = new string[dt2.Rows.Count];
for (int a2 = 0; a2 < dt2.Rows.Count; a2++)
{
array2[a2] = dt2.Rows[a2]["stud_Id"].ToString();
SqlCommand scmd3 = new SqlCommand();
}
}
In my first SQL statement I have selected those who have best percentage and those whose who passed and stored in an array.
With the for loop I am retrieving the data table value
In the second SQL statement, I have made a join with tblAcademy and tblAcademy_selection where the tblAcademy_selection.stud_id is in the retrieve value that I have done in the first statement.
I am having difficulty to apply the condition in which if an student choice of academy seat is full it move to the second choice and if the second is full it move to the third and so on.
A student may not have academy if all his choice academy seat is full.

Answer 1

You have to apply a filter condition in your SQL statement to filter out records with tblAcademy.seat_available = 0.
Then generate a row_number or rank based on order preference and retrieve records with generated row_number =1.
Something like this:
SELECT * 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.seat_available >0 and stud_Id IN ('" + array[a] + "')"
) DTL
WHERE row_id = 1