c#如何用select count统计记录数并赋值给变量？又如何输出统计数变量？

可用下面的方法:
存储过程+c#代码调用。

示例代码：
private void button1_Click(object sender, EventArgs e)
{

string connectionString = "server=sqlServerName;user id=userID;" +
"password= yourPwd;initial catalog=dbName";

DataSet MyDataSet = new DataSet();
System.Data.SqlClient.SqlDataAdapter DataAdapter = new System.Data.SqlClient.SqlDataAdapter();

System.Data.SqlClient.SqlConnection myConnection = new System.Data.SqlClient.SqlConnection(connectionString);
if (myConnection.State != ConnectionState.Open)
{
myConnection.Open();
}
System.Data.SqlClient.SqlCommand myCommand = new System.Data.SqlClient.SqlCommand("Pro_GetStudentInfo", myConnection);
myCommand.CommandType = CommandType.StoredProcedure;
//添加输入查询参数、赋予值
myCommand.Parameters.Add("@myName", SqlDbType.VarChar);
myCommand.Parameters["@myName"].Value = "li";

//添加输出参数
myCommand.Parameters.Add("@Rowcount", SqlDbType.Int);
myCommand.Parameters["@Rowcount"].Direction = ParameterDirection.Output;

myCommand.ExecuteNonQuery();
DataAdapter.SelectCommand = myCommand;

if (MyDataSet != null)
{
DataAdapter.Fill(MyDataSet, "table");
}

this.dataGridView1.DataSource = MyDataSet.Tables[0];

//得到存储过程输出参数
MessageBox.Show( myCommand.Parameters["@Rowcount"].Value.ToString());

if (myConnection.State == ConnectionState.Open)
{
myConnection.Close();
}

}
建库脚本:
create table student
(
id varchar(20),
name varchar(50)
);
go
insert into student values('1','wang');
insert into student values('2','li');
insert into student values('3','li');
go

CREATE PROC Pro_GetStudentInfo
@myName VARCHAR(20),
@Rowcount INT OUTPUT
AS
BEGIN
set @Rowcount=( SELECT count(*) FROM student WHERE name=@myName);

SELECT * FROM student WHERE name=@myName;

END
GO