C#用LINQ *** 作Datatable数据库

假设你上图表格数据为 DataTable dt，列分别为AA,BB,CC,DD

var query = from p in dt.AsEnumerable()

//分组

group p by new

{

t1 = p.Field<int>("AA").ToString().Substring(0, p.Field<int>("AA").ToString().Length - 2),

t2 = p.Field<double>("BB"),

t3 = p.Field<string>("CC")

} into g

select new

{

ColA = g.Key.t1,

ColB = g.Key.t2,

ColC = g.Key.t3,

ColD = g.Sum(c =>c.Field<int>("DD"))

}

//转datatable

DataTable dtNew = dt.Clone()

DataRow drNew

foreach (var p in query)

{

drNew = dtNew.NewRow()

drNew["AA"] = p.ColA

drNew["BB"] = p.ColB

drNew["CC"] = p.ColC

drNew["DD"] = p.ColD

dtNew.Rows.Add(drNew)

}

dtNew 为最终结果

注：转换过程中要考虑空值的情况

c#连接MySql数据库的方法

一、用MySQLDriverCS连接MySQL数据库。

先下载和安装MySQLDriverCS，在安装文件夹下面找到MySQLDriver.dll，然后将MySQLDriver.dll添加引用到项目中。

using System

using System.Collections.Generic

using System.ComponentModel

using System.Data

using System.Drawing

using System.Linq

using System.Text

using System.Windows.Forms

using MySQLDriverCS

namespace jxkh

{

public partial class frmLogin : Form

{

public frmLogin()

{

InitializeComponent()

}

private void btnLogin_Click(object sender, EventArgs e)

{

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