求助求大神帮忙C#数据库添加功能

求大神给个代码

private void button2_Click(object sender, EventArgs e)
{
String str = "Server=.;DataBase=kebiao;Integrated Security=true;";
SqlConnection conn = new SqlConnection(str);
String s3 = textBox7.Text;
string str3 = "delete from kebao where xm=' " + s3 + "'";
SqlCommand cmd = new SqlCommand();
cmd.Connection = conn;
cmd.CommandText = str3;
conn.Open();
cmd.ExecuteNonQuery();
conn.Close();
}

这是我删除的功能代码，，运行不报错，也不删除，是为什么

数据库名称：kebiao 表的名称：kebao
xm是列名 C#里面输入xm的是 textBox7