左连接Mysql查询导致错误

我有一个MySQL左连接查询。这个查询运行正常。但是左边的加入表没有获得价值。请通过以下查询。我工作在C＃左连接Mysql查询导致错误

void getstuinfo() 
     { 
      try 
      { 
       MySqlCommand com = new MySqlCommand("select stumaster.stuname,"+ 
       "stumaster.lname,"+ 
       "stumaster.fname,"+ 
       "stumaster.mname,"+ 
       "stumaster.fa_calty,"+ 
       "stumaster.sex,"+ 
       "castmaster.castdisp,"+ 
       "stumaster.castcode,"+ 
       "stumaster.nwscs "+ 
       "from stumaster "+ 
       " left join castmaster on stumaster.castcode = castmaster.castcode "+ 
       " where grno = " + Convert.ToInt32(textBox1.Text).ToString(), con_db.con); 
       MySqlDataReader dr1 = com.ExecuteReader(); 
       if (dr1.HasRows) 
       { 
        while (dr1.Read()) 
        { 
         textBox2.Text = (dr1[("stuname")].ToString()); 
         textBox4.Text = (dr1["lname"]).ToString(); 
         textBox5.Text = (dr1["fname"]).ToString(); 
         textBox6.Text = (dr1["mname"]).ToString(); 
         comboBox5.Text = (dr1["fa_calty"]).ToString(); 
         comboBox1.Text = (dr1["castdisp"]).ToString(); 
         textBox7.Text = (dr1["castcode"]).ToString(); 
         textBox9.Text = (dr1["nwscs"]).ToString(); 
         string wsex = (dr1["sex"]).ToString(); 

         if (wsex == "M") 
         { 
          radioButton1.Checked = true; 
         } 
         else 
         { 
          radioButton2.Checked = true; 
         } 
        } 
        dr1.Close(); 
       } 
       else 
       { 
        MessageBox.Show("Not a Valid G.R.No.", " Student Information "); 
        dr1.Close(); 
        textBox1.Focus(); 
        return; 
       } 
      } 
      catch (FormatException) 
      { 
       MessageBox.Show("Date is Invalid "); 
      } 
     }

来源

2017-03-23 Anand Coolkarni

给表名可以提供输出？ – jarg

你有grno

即

stumaster.grno = conditiion

来源

2017-03-23 07:10:22

感谢您的重播。我已纠正它，但没有结果。意味着它没有显示“castmaster.castdisp”值休息查询执行正常。 –

如果所有的值都填充然后检查枯萎castdisp是否有价值或不知道mysql的sql bt我们使用isnull（castdisp，0）意味着如果值为null，那么用0替换该列的结果 –

检查枯萎的列有一个值或不是因为c＃会做什么，它会将null更改为空字符串，这可能是因为您正在使用左外部连接而不是仅获取该列中的数据的原因，它还将包括NULL值 –

左连接Mysql查询导致错误

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