C# 如何使用c查找SQL Server中的值是否为NULL#

我想知道从SqlHelper类的ExecuteDataTable返回的c#中的datatable中哪些值为null

string select = "select * from testTable";
string val="";

DataTable  dt=dbcon.ExecuteDataTable(select);
foreach (DataRow dr in dt.Rows)
{
   foreach (DataColumn  dc in dt.Columns )
   {
       if(dr[dc].Equals (null))
       {
          val ="null";
       } 
       else  
       {
          val = dr[dc].ToString();
       }
   }
}

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但不幸的是，我没有找到任何方法。如果有办法，请告诉我。提前谢谢。

您需要

DBNull.Value

：

if (dr[dc] == DBNull.Value)

---

除David M的方法外，您还可以使用：

如果（dr[dc]==DBNull.Value）有效！ 这就是我需要它的原因。它为给定的表名生成插入脚本

String tableName= "mytable";

           string select = "select * from "+tableName ;
           DataTable  dt=dbcon.ExecuteDataTable(select );
           StringBuilder sb = new StringBuilder();
           string pk="";

           sb.AppendFormat ( "select Name from sys.columns where Object_ID = Object_ID('{0}') and is_identity=1",tableName );
           try
           {
               pk = dbcon.ExecuteScalar(sb.ToString()).ToString();
           }
           catch
           { }
           sb.Remove(0, sb.Length);
            foreach (DataRow dr in dt.Rows  )
            {
                sb.Append("Insert INTO " + tableName + " VALUES( ");
                foreach (DataColumn  dc in dt.Columns )
                {
                    if (dc.ColumnName != pk)
                    {
                        string val = dr[dc].ToString();

                        if (dr[dc] == DBNull.Value)
                        {
                            sb.AppendFormat("{0} , ", "null");
                        }
                        else
                        {
                            sb.AppendFormat("'{0}' , ", dr[dc].ToString());
                        }
                    }
                }
                sb.Remove(sb.Length - 2, 2);
                sb.AppendLine(")");
            }

---

我会使用它，因为它的IL略少，效率略高（在处理数据时这是个好主意）。

String tableName= "mytable";

           string select = "select * from "+tableName ;
           DataTable  dt=dbcon.ExecuteDataTable(select );
           StringBuilder sb = new StringBuilder();
           string pk="";

           sb.AppendFormat ( "select Name from sys.columns where Object_ID = Object_ID('{0}') and is_identity=1",tableName );
           try
           {
               pk = dbcon.ExecuteScalar(sb.ToString()).ToString();
           }
           catch
           { }
           sb.Remove(0, sb.Length);
            foreach (DataRow dr in dt.Rows  )
            {
                sb.Append("Insert INTO " + tableName + " VALUES( ");
                foreach (DataColumn  dc in dt.Columns )
                {
                    if (dc.ColumnName != pk)
                    {
                        string val = dr[dc].ToString();

                        if (dr[dc] == DBNull.Value)
                        {
                            sb.AppendFormat("{0} , ", "null");
                        }
                        else
                        {
                            sb.AppendFormat("'{0}' , ", dr[dc].ToString());
                        }
                    }
                }
                sb.Remove(sb.Length - 2, 2);
                sb.AppendLine(")");
            }