SqlDataAdapter使用显示缺少using指令集


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;namespace WindowsFormsApplication2
{
    public partial class main : Form
    {
        public main()
        {
            InitializeComponent();
        }        private void select_Click(object sender, EventArgs e)
        {
            implement();
        }
        private void implement()
        {
            string IPAdress = "";
            string DBUid = "";
            string DBPwd = "";
            IPAdress = this.IPAdress.Text;
            DBUid = this.DBUid.Text;
            DBPwd = this.DBPwd.Text;
            string sql1="Data Source=";
            string sql2=";Database=CounterDB;Uid=";
            string sql3=";Pwd=";
            string sqlconn = sql1 + IPAdress + sql2 + DBUid + sql3 + DBPwd;
            SqlConnection conn = new SqlConnection(sqlconn);
            conn.Open();
            DataSet ds = new DataSet();
            SqlDataAdapter da = new SqlDataAdapter();
            da.SelectCommand sc = new SqlCommand("select * from FactSitesPerformance", conn);
            da.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];
            conn.Close();
            MessageBox.Show("数据库连接成功");
            MessageBox.Show(sqlconn);
        }
    }
}在da.SelectCommand sc = new SqlCommand("select * from FactSitesPerformance", conn);中
da提示缺少指令集，请各位大神指教，怎么解决这个问题。C#SQL