how to save database data using foreach loop in console

Question

 In table record as follows

Select * from Employee

Cityid AssName ProjectName Mobile Source Destination
1 Rakesh Java 987445 TK BLR
1 Suresh Dotnet 884554 RM BTP
1 Vignesh Testing 451211 RP KOL
1 Suresh Mainframe 457845 RF KOL

2 Ramesh Animation 454542 JS KOC
2 Magesh Warehouse 211455 WH KOC
2 Santhosh Database 445545 RO CHN
2 Vignesh ETLTool 154555 VJ CHN


console application code as follows

i am displaying the above data from table Employee(Database) in to excel file using console application.

My console application code as follows


string connectionstring = "Server=(local);initial catalog=OneC;Trusted_Connection=True";
SqlConnection con = new SqlConnection(connectionstring);
SqlCommand command= new SqlCommand();
SqlDataReader dr;
DataSet ds= new DataSet();
command.CommandText = "Select * from Employee";
command.CommandType = CommandType.Text;
command.Connection = con;
con.Open();
dr= cmd.ExecuteReader();
if (dr.HasRows)
{

using (System.IO.StreamWriter sw = new System.IO.StreamWriter(@"C:\Details\Excel.xls"))
{
while (dr.Read())
{
for (int i = 0; i < dr.FieldCount; i++)
{
sw.Autoflush = true;
sw.write(dr[i].Tostring() + "\t");
}
sw,writeline("\n");
}
}
con.Close();
}


When i exeucte above query in my system in c folder under the folder details excel file is created as follows

in my system C Folder created as details in that details folder excel file is created a
1 Rakesh Java 987445 TK BLR
1 Suresh Dotnet 884554 RM BTP
1 Vignesh Testing 451211 RP KOL
1 Suresh Mainframe 457845 RF KOL

2 Ramesh Animation 454542 JS KOC
2 Magesh Warehouse 211455 WH KOC
2 Santhosh Database 445545 RO CHN
2 Vignesh ETLTool 154555 VJ CHN


But i want excel file to be saved based on city id. The city id 1 details to be saved in one excel

And another city id 2 details to be saved in another excel


for that how can i do in asp.net using my above code in console application

I want City id 1 details to be saved in one excel as follows

1 Rakesh Java 987445 TK BLR
1 Suresh Dotnet 884554 RM BTP
1 Vignesh Testing 451211 RP KOL
1 Suresh Mainframe 457845 RF KOL


I want City id 2 details to be saved in another excel as follows

2 Ramesh Animation 454542 JS KOC
2 Magesh Warehouse 211455 WH KOC
2 Santhosh Database 445545 RO CHN
2 Vignesh ETLTool 154555 VJ CHN