我想实现的是在往数据库中插入内容的时候，首先对要插入的内容进行验证，看数据库是否存在，我采用的是从gridview中先提取它的货号进行比较，但是我就是不知道怎么用代码实现和数据库中的货号比较，

那不就和做注册检查用户名存在的一个道理吗？
sqlcommand comm=new sqlcommand(select count(货号) from 表 where 货号字段=要检查的货号，conn)；
int a=convert.toint32(comm.exevutscalar());
if(a>0)
{存在}
else
{不存在}

protected void btchaxun_Click(object sender, EventArgs e)
    {

        SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
        conn.Open();

        SqlCommand mycommand = new SqlCommand("select count(*) from commoditylist where goodsno ='" + huohao + "'", conn);
       int count = Convert.ToInt32(mycommand.ExecuteScalar());
        if (count > 0)
        {

            lb1.Text = "查无此货";

        }
        else
        {

           // SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
           // conn.Open();

            SqlDataAdapter comm = new SqlDataAdapter("select * from commoditylist where goodsno= " + Convert.ToInt32(huohao.Text), conn);
            DataSet dc = new DataSet();
            comm.Fill(dc, "commoditylist");
            dr = dc.Tables["commoditylist"].Rows[0];


            pinming.Text = dr["hname"].ToString();
            guige.Text = dr["specifications"].ToString();
            chandi.Text = dr["origin"].ToString();
            DropDownList1.SelectedItem.Text = dr["categories"].ToString();
            jinhuojia.Text = dr["stockprice"].ToString();
            xiaoshoujia.Text = dr["saleprice1"].ToString();
            zuidishoujia.Text = dr["minimumsaleprice"].ToString();
            kucunxiaxian.Text = dr["kcxx"].ToString();
            beizhu.Text = dr["note"].ToString();


        }

    }
我是这样写的啊 但是它总是报错啊

刚才的写错了


 protected void btchaxun_Click(object sender, EventArgs e)
    {

        SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
        conn.Open();

        SqlCommand mycommand = new SqlCommand("select count(*) from commoditylist where goodsno ='" + huohao + "'", conn);
        //int count = Convert.ToInt32(mycommand.ExecuteScalar());
        if (count > 0)
        {
//SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
           // conn.Open();

            SqlDataAdapter comm = new SqlDataAdapter("select * from commoditylist where goodsno= " + Convert.ToInt32(huohao.Text), conn);
            DataSet dc = new DataSet();
            comm.Fill(dc, "commoditylist");
            dr = dc.Tables["commoditylist"].Rows[0];


            pinming.Text = dr["hname"].ToString();
            guige.Text = dr["specifications"].ToString();
            chandi.Text = dr["origin"].ToString();
            DropDownList1.SelectedItem.Text = dr["categories"].ToString();
            jinhuojia.Text = dr["stockprice"].ToString();
            xiaoshoujia.Text = dr["saleprice1"].ToString();
            zuidishoujia.Text = dr["minimumsaleprice"].ToString();
            kucunxiaxian.Text = dr["kcxx"].ToString();
            beizhu.Text = dr["note"].ToString();


     

         
        }
        else
        {  lb1.Text = "查无此货";

   }
            
    }

运行侯的错误是

int count = Convert.ToInt32(mycommand.ExecuteScalar());这一行

将 varchar 值 'System.Web.UI.WebControls.TextBox' 转换为数据类型为 int 的列时发生语法错误。

SqlDataAdapter comm = new SqlDataAdapter("select * from commoditylist where goodsno= " + Convert.ToInt32(huohao.Text), conn);
应该是这行的错误吧……
不是说将 varchar 值 'System.Web.UI.WebControls.TextBox' 转换为数据类型为 int 的列时发生语法错误吗？
你看你写的对不对啊，是不是疏忽了引号啊……
SqlDataAdapter comm = new SqlDataAdapter("select * from commoditylist where goodsno= '" + Convert.ToInt32(huohao.Text)+"'", conn);

不是那个问题啊 ，我照你的方法做了 还是那句出错啊

那句有什么错误啊……
那句不应该有那样的错误吧……

奥……
找到了……
 SqlCommand mycommand = new SqlCommand("select count(*) from commoditylist where goodsno ='" + huohao + "'", conn);
这句是不是应该给huohao加上给huohao.text.toint32()
要是你的goodsno是字符那么就是huohao.text.tostring()

protected void queding_Click(object sender, EventArgs e)
    {
        if ( pinming.Text== "" && guige.Text == "" && chandi.Text =="" && jinhuojia.Text == ""&& xiaoshoujia.Text == "" && zuidishoujia.Text == "" && kucunxiaxian.Text == "" && beizhu.Text == "")
        {

            Response.Write("<script language='javascript'>alert('不能添加空项！')</script>");
            return;

        }


        if (exist())
        {
            // this.Label1.Text = "";
            Response.Write("<script language='javascript'>alert('该商品已经存在！')</script>");
        }
        else
        {
            insert();
        }
    }
        private Boolean exist()
    {
        SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
        conn.Open();
         SqlCommand mycommand = new SqlCommand("select * from commoditylist where hname ='" + pinming.Text + "'", conn);
        SqlDataReader dd;
        dd = mycommand.ExecuteReader();
        if (dd.HasRows)
        {
            return true;
        }
        else
        {
            return false;
        }
      
      
   
    }
    private void insert()
    {
        SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["ConStr"]);
        conn.Open();
        SqlCommand comm = new SqlCommand("insert into commoditylist values ( '" + pinming.Text.ToString() + "','"+ guige.Text.ToString() + "', '" + chandi.Text.ToString() + "','" + DropDownList1.SelectedItem.Value + "', '" + jinhuojia.Text + "', '" + xiaoshoujia.Text + "' ,'" + zuidishoujia.Text + "','" + kucunxiaxian.Text + "','" + beizhu.Text.ToString() + "')", conn);
        
        comm.ExecuteNonQuery();
        conn.Close();
        Response.Redirect("ziliao.aspx");这样做验证就对了，谢谢你的帮忙，