NET 2.0開始有這個功能,可以批次寫入.
我們做個簡單範例,把來源讀到的data table,新增到Target去.

建立測試資料表 source & target

--source
create table test_src
(
src1 int
,src2 int
,src3 int
)
insert into test_src select 1,1,1
insert into test_src select 2,2,2
insert into test_src select 3,3,3
--target
create table test_dest
(
COL1 int
,COL2 int
,COL3 int
)

執行

       System.Data.DataTable dt =      getsrc();//取來源
       BulkCopy(dt);//寫入

取來源

        private System.Data.DataTable getsrc()
        {
            System.Data.DataTable dt = new System.Data.DataTable();
            string sConn = "data source = xxx  ;initial catalog= db; user id = sa ;password= sa ";
            using (SqlConnection conn = new SqlConnection(sConn))
            {
                conn.Open();
                SqlDataAdapter adp = new SqlDataAdapter("select * from test_src", conn);
                adp.Fill(dt);                
            }
            return dt;
        }

寫入

 private void  BulkCopy( System.Data.DataTable dt)
 {
            //  整批轉入
            string sConn = "data source = xxx  ;initial catalog= db; user id = sa ;password= sa ";

            using (SqlConnection conn = new SqlConnection(sConn))
            {
                conn.Open();
                using (SqlBulkCopy sqlBC = new SqlBulkCopy(conn))
                {
                    //設定一個批次量寫入多少筆資料
                    sqlBC.BatchSize = 1000;
                    
                    //設定逾時的秒數
                    sqlBC.BulkCopyTimeout = 60;

                    //設定要寫入的資料庫
                    sqlBC.DestinationTableName = "test_dest";

                    //對應資料行
                    sqlBC.ColumnMappings.Add("src1", "COL1");
                    sqlBC.ColumnMappings.Add("src2", "COL2");
                    sqlBC.ColumnMappings.Add("src3", "COL3"); 

                    //開始寫入
                    sqlBC.WriteToServer(dt);
                }
            }
 } 

對應資料行的部分,也可以把dt的改成和dest一樣,這樣ColumnMappings就不用因不同的來源,而變動.
dt.Columns[0].ColumnName = "COL1";
dt.Columns[1].ColumnName = "COL2";
dt.Columns[2].ColumnName = "COL3";
ref
https://dotblogs.com.tw/supershowwei/2016/12/09/221622

換個方式寫一下,欄位相同不用寫對應.

取來源

        private System.Data.DataTable getsrc()
        {
            System.Data.DataTable dt = new System.Data.DataTable();
            string sConn = "data source = xxx  ;initial catalog= db; user id = sa ;password= sa ";
            using (SqlConnection conn = new SqlConnection(sConn))
            {
                conn.Open();
                SqlDataAdapter adp = new SqlDataAdapter("select 1,2,3", conn);
                adp.Fill(dt);                
            }
            return dt;
        }
 
  private void  BulkCopy( System.Data.DataTable dt)
 {
            //  整批轉入
            string sConn = "data source = xxx  ;initial catalog= db; user id = sa ;password= sa ";

            using (SqlConnection conn = new SqlConnection(sConn))
            {
                conn.Open();
                using (SqlBulkCopy sqlBC = new SqlBulkCopy(conn))
                {
                    //設定一個批次量寫入多少筆資料
                    sqlBC.BatchSize = 1000;
                    
                    //設定逾時的秒數
                    sqlBC.BulkCopyTimeout = 60;

                    //設定要寫入的資料庫
                    sqlBC.DestinationTableName = "test_dest"; 
                    //開始寫入
                    sqlBC.WriteToServer(dt);
                }
            }
 }           

reader的方式

https://blog.gss.com.tw/index.php/2018/08/08/sqlbulkcopy/