数据库查询主码存在与否

Question

如果存在主码则弹框，不存在则继续。SqlCommand one = new SqlCommand("select version from t_version_base where version='" + textBox2.ToString() + "'", conn);                one.CommandType = CommandType.Text;
                one.ExecuteNonQuery();
                SqlDataReader dr = null;
                dr = one.ExecuteReader();
                while (dr.Read())
                {
                    if (dr["version"] != null)
                    {                        string str = dr["version"].ToString();                        if (str.ToString() == textBox2.ToString())
                        {
                            MessageBox.Show("hhhhhhhhhhhhhhhhhhh");
                        }                        dr.Close();
                    }
                }
testbox2.tostring 是输入的主码，怎样读取数据库查询结果并比较？

Answer 1

SqlCommand one = new SqlCommand("select count(1) from t_version_base where version='" + textBox2.ToString() + "'", conn);
int count = (int)one.ExecuteScalar();
if(count > 0){
MessageBox.Show("hhhhhhhhhhhhhhhhhhh");
}else{
// continue;
}

Answer 2

SqlCommand one = new SqlCommand("select version from t_version_base where version='" + textBox2.ToString() + "'", conn);                one.CommandType = CommandType.Text;
                one.ExecuteNonQuery();//这句是多余的
                SqlDataReader dr = null;
                dr = one.ExecuteReader();
                while (dr.Read())
                {
                    if (dr["version"] != null)
                    {                        string str = dr["version"].ToString();
                        //str本来就是string，不同ToString()了，取文本框的值用Text属性
                        if (str.ToString() == textBox2.Text)
                        {
                            MessageBox.Show("hhhhhhhhhhhhhhhhhhh");
                        }                        dr.Close();
                    }
                }