using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TestConsole
{
    /// <summary>
    /// 測試類
    /// </summary>
    [Serializable]
    public class TestDemo
    {
        
 
/// <summary>
        /// 數據庫連接字符串
        /// </summary>
        private readonly string connectionString = "server=.;database=TestDB;uid=sa;pwd=123456";

        /// <summary>
        /// 從數據庫中查詢所有記錄
        /// </summary>
        /// <returns></returns>
        private DataTable GetTableFromDatabase()
        {
            
 
using (SqlConnection conn = new SqlConnection(connectionString))
            {
                try
                {
                    conn.Open();
                    SqlDataAdapter sda = new SqlDataAdapter("select Id,Name,ValueA,ValueB from TestTable", conn);
                    DataSet ds 
 
= new DataSet();
                    sda.Fill(ds);

                    DataTable dbTable = null;
                    if (ds != null)
                    {
                        dbTable = ds.Tables[0];
                    }
                    return dbTable;
                }
                catch (Exception e)
                {
                    throw e;
                }
            }
        }

        /// <summary>
        /// 修改
        /// </summary>
        /// <param name="value"></param>
        /// <param name="nameValue"></param>
        private void Update(int value, string nameValue)
        {
            string updateSql = "update TestTable set ValueA=" + value + " where Name=‘" + nameValue + "‘";
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(updateSql, conn))
                {
                    try
                    {
                        conn.Open();
                        int rows = cmd.ExecuteNonQuery();
                    }
                    catch (System.Data.SqlClient.SqlException e)
                    {
                        conn.Close();
                        throw e;
                    }
                }
            }
        }

        /// <summary>
        /// 從內存獲取DataTable
        /// </summary>
        /// <returns></returns>
        private DataTable GetTableFromMemory()
        {
            DataTable dt = new DataTable("TestTable");
            dt.Columns.Add("Id", typeof(System.Int32));
            dt.Columns.Add("Name", typeof(System.String));
            dt.Columns.Add("ValueA", typeof(System.Int32));
            dt.Columns.Add("ValueB", typeof(System.String));

            DataRow row;

            row = dt.NewRow();
            row["Id"] = 1;
            row["Name"] = "ItemA";
            row["ValueA"] = 20;
            dt.Rows.Add(row);

            row = dt.NewRow();
            row["Id"] = 67;
            row["Name"] = "ItemC";
            row["ValueA"] = 90;
            dt.Rows.Add(row);

            return dt;
        }

        /// <summary>
        /// 測試方法
        /// </summary>
        public void TestMethod()
        {
            String nameValue = "ItemC";

            //從內存獲取DataTable，並找到值為ItemC的記錄
            DataTable memoryTable = GetTableFromMemory();
            DataRow[] memoryArr = memoryTable.Select("Name=‘" + nameValue + "‘");
            int valueA = 0;
            int.TryParse(memoryArr[0]["ValueA"].ToString(), out valueA);

            //將內存表中Name=ItemC的ValueA更新到數據表中
            Update(valueA, nameValue);

            //將數據庫中的ValueB數據欄及其對應的值添加到內存表中
            DataTable dbTable = GetTableFromDatabase();
            if (dbTable != null && dbTable.Rows.Count > 0)
            {
                //遍歷數據表中的記錄
                foreach (DataRow dr in dbTable.Rows)
                {
                    DataRow[] tempDR = memoryTable.Select("Name=‘" + dr["Name"] + "‘");
                    if (tempDR.Length > 0)
                    {
                        tempDR[0]["ValueB"] = dr["ValueB"];
                    }
                    else
                    {
                        DataRow row = memoryTable.NewRow();
                        row["Id"] = dr["Id"];
                        row["Name"] = dr["Name"];
                        row["ValueA"] = dr["ValueA"];
                        row["ValueB"] = dr["ValueB"];
                        memoryTable.Rows.Add(row);
                    }
                }
            }
        }
    }
}

一段用c#操作datatable的代碼