用c#从oracle数据库中检索值

本文关键字：检索 数据库 oracle | 更新日期: 2023-09-27 18:02:29

我不知道为什么，但我得到一个错误，试图从一个表在oracle数据库中获得最大的整数值:以下是代码:

string oradb = "Data Source=";
            oradb = oradb + Login.db + ";";
            oradb = oradb + "User Id=" + Login.user;
            oradb = oradb + ";Password=" + Login.pass + ";";
            OracleConnection conn = new OracleConnection(oradb);
            conn.Open();
            string term = GetTerminal(terminal);
            string sql = "SELECT tallynumber from "+frmSchemas.schema + ".tallies" ;
             MessageBox.Show(sql);
            OracleCommand cmd = new OracleCommand(sql, conn);
            cmd.CommandType = CommandType.Text;
            OracleDataReader dr = cmd.ExecuteReader();
            MessageBox.Show("1");
            Int64 TallyNo = dr.GetInt32(0);  

      // lblTallyNo.Text = (TallyNo).ToString()

返回值应该是:72332

用c#从oracle数据库中检索值

您可以尝试使用以下

        string sql = "SELECT max(tallynumber) from "+frmSchemas.schema + ".tallies" ;
         MessageBox.Show(sql);
        OracleCommand cmd = new OracleCommand(sql, conn);
        cmd.CommandType = CommandType.Text;
        OracleDataReader dr = cmd.ExecuteReader();
        MessageBox.Show("1");
        if (dr.Read())
        {
        Int64 TallyNo = dr.GetInt32(0); 
        }
编辑:

if(dr.Read())
{
Int64 TallyNo = Convert.ToInt64(dr["tallynumber"].ToString());
}

在访问值

之前缺少一个dr.Read();
OracleDataReader dr = cmd.ExecuteReader();
dr.Read();
Int64 TallyNo = dr.GetInt32(0);

如果你想从一个table中找到max value，那么query应该是

SELECT max(tallynumber) from ....

如果你想获得max, min etc的值，你应该调用ExecuteScalar()而不是ExecuteReader().

所以你的代码可以变成 
   string sql = "SELECT Max(tallynumber) from "+frmSchemas.schema + ".tallies";              MessageBox.Show(sql);             
    OracleCommand cmd = new OracleCommand(sql, conn);             
    cmd.CommandType = CommandType.Text;             
    object val = cmd.ExecuteScalar();
int res = int.MinValue;             
    //MessageBox.Show("1");
  if(int.TryParse(val.ToString(), out res)) 
    Int64 TallyNo = res;
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