C#代码连接SQL Server数据库

class SqlExecute
{
private string connectionString;
private SqlConnection conn;
private SqlCommand cmd;
private SqlDataAdapter adapter;
private SqlDataReader reader;
private DataSet dataset;
public SqlExecute()
{
connectionString = "server=localhost;uid=sa;pwd=saas;database=stu";
}
private void getStatement()
{
try
{
connectionString = "server=localhost;uid=sa;pwd=saas;database=stu";
conn = new SqlConnection(connectionString);
conn.Open();
}
catch(Exception e)
{

}
}
public void closeData()
{
try
{
if(conn.State == ConnectionState.Open)
conn.Close();

}
catch(Exception e)
{

}

}
public int newDataUpdate(string sql)
{
getStatement();
cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.Connection = conn;
cmd.CommandText = sql;
int i = cmd.ExecuteNonQuery();
return i;
}
public DataSet sqlQuery(string sql)     //查询数据
{
adapter = new SqlDataAdapter(sql,connectionString);
dataset = new DataSet();
adapter.Fill(dataset);
return dataset;
}
public void fillGrid(string sql,DataGridView dgv)       //填充GridView
{
DataSet ds = sqlQuery(sql);
dgv.DataSource = ds.Tables[0];
}
}