coun(*)返回值有关问题_ASP.NET

coun(*)返回值问题？

C# code

private void _btn()    {        string sql = "select count(*) from [dhk_qiankuan] where user_name='" + ddl_name.SelectedItem.Text + "'";        SqlConnection con = new SqlConnection(conString);        con.Open();        SqlCommand cmd = new SqlCommand(sql, con);        int sum = (int)cmd.ExecuteNonQuery();        if (sum == 0)        {            btn_submit.Visible = false;        }        else        {            btn_submit.Visible = true;        }    }

为什么返回空btn_submit 也等于true?

------解决方案--------------------------------------------------------
查询要用(int)cmd.ExecuteScalar()

C# code

private void _btn()    {        string sql = "select count(*) from [dhk_qiankuan] where user_name='" + ddl_name.SelectedItem.Text + "'";        SqlConnection con = new SqlConnection(conString);        con.Open();        SqlCommand cmd = new SqlCommand(sql, con);        int sum = (int)cmd.ExecuteScalar();        if (sum == 0)        {            btn_submit.Visible = false;        }        else        {            btn_submit.Visible = true;        }    }
------解决方案--------------------------------------------------------
int sum = (int)cmd.ExecuteNonQuery();换成
int sum = (int)cmd.ExecuteScalar();
------解决方案--------------------------------------------------------
ExecuteNonQuery不是用了执行select语句的，你用ExecuteScalar得到count值来判断
------解决方案--------------------------------------------------------
ExecuteNonQuery 返回的是受影响的行数.