Question

我正在创建学生出勤信息系统。

如您所见，这些方法彼此相关。 students表有关于每个学生的一般信息。有些学生总是缺席，所以register表中没有students_ID。这导致da.Fill（dt）出错。它说：

MySqlException未被用户代码＆＃34处理;您的错误 SQL语法;查看与MySQL服务器对应的手册正确使用语法的版本＆＃39;）＆＃39;在第1行＆＃34;

如何消除此错误？

private string getUquvchilar_ID()
{
    var fish = ddlName.Text.Replace("'", "''");
    MySqlConnection con = new MySqlConnection(constr);
    con.Open();
    string query = "Select Students_ID from students where CONCAT(Familiyasi , ' ', Ismi , ' ', Sharifi)='" + fish + "'";
    MySqlCommand cmd = new MySqlCommand(query);
    cmd.Connection = con;
    String s = (cmd.ExecuteScalar() ?? String.Empty).ToString();
    con.Close();
    return s;
}
private void BindGrid()
{
    MySqlConnection con = new MySqlConnection(constr);
    MySqlCommand cmd = new MySqlCommand("SELECT * FROM rasmlar where Rasm_ID in (" + String.Join(",", getImage_ID()) + ")", con);
    MySqlDataAdapter da = new MySqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    da.Fill(dt);
    gvImages.DataSource = dt;
    gvImages.DataBind();
}
private List<int> getImage_ID()
{
    List<int> i = new List<int>();
    MySqlConnection con = new MySqlConnection(constr);
    con.Open();
    string query = "Select bosh_rasm_ID, Tugal_rasm_ID from register where students_ID='" + getUquvchilar_ID() + "'"; 
    MySqlCommand cmd = new MySqlCommand(query);
    cmd.Connection = con;
    MySqlDataReader reader = cmd.ExecuteReader();
    if (reader != null && reader.HasRows)
    {
        foreach (DbDataRecord s in reader)
        {
            if (!reader.IsDBNull(reader.GetOrdinal("bosh_rasm_ID")))
                i.Add(s.GetInt32(0));
            else
                i.Add(0);
            if (!reader.IsDBNull(reader.GetOrdinal("Tugal_rasm_ID")))
                i.Add(s.GetInt32(1));
            else
                i.Add(0);
        }
    }
    return i;
}

Answer 1

如果getImage_ID（）返回一个空列表，那么select语句将是SELECT * FROM rasmlar where Rasm_ID in () ...这是一个无效的sql语句......你必须明确处理这个案例。

string方法null在其他方法的select查询中

1 个答案: