Get summarized/sorted data from SQL Server in ASP.NET - sql

Question

below is my sql table in which I'm saving student attendance
I'm trying to create a summarized attendance report as below:
Attendance Summary of all students:
Number of students present in class I: 1
Number of students present in class II: 1
Number of students present in class III: 0
But I don't exactly am finding a right way to do it. below is the sample code I'm trying to use to achieve this:
public void GetPresentCount()
{
using (SqlConnection con = new SqlConnection(constring))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("select count(*) as 'TotalPresent' from stud_att where att='Present' and a_date='"+ systemdate +"'", con))
{
using (SqlDataReader dr = cmd.ExecuteReader())
{
if (dr.Read())
{
totstuds.InnerText = dr["TotalCount"].ToString();
}
else
{
totstuds.InnerText = "0";
}
}
}
con.Close();
}
}
public void GetAbsentCount()
{
using (SqlConnection con = new SqlConnection(constring))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("select count(*) as 'TotalPresent' from stud_att where att='Present' and a_date='" + systemdate + "'", con))
{
using (SqlDataReader dr = cmd.ExecuteReader())
{
if (dr.Read())
{
totstuds.InnerText = dr["TotalCount"].ToString();
}
else
{
totstuds.InnerText = "0";
}
}
}
con.Close();
}
}
But I know this is not the right way.

Answer 1

I think you just want conditional aggregation:
select class,
sum(case when att = 'Present' then 1 else 0 end) as attendance
from stud_att
where a_date = ?
group by class
order by class;
The ? is a parameter placeholder to pass in the date. Don't munge SQL queries with constant values; pass them in as parameters.