设计时实现的分组统计:

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运行时实现的分组统计:

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//前期只需要添加 ClientDataSet1、DataSource1、DBGrid1; 事件只需要关联窗体的 OnCreate

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Grids, DBGrids, DB, DBClient;

type
  TForm1 = class(TForm)
    DBGrid1: TDBGrid;
    DataSource1: TDataSource;
    ClientDataSet1: TClientDataSet;
    procedure FormCreate(Sender: TObject);
  private
    procedure OnGetText_Agg1(Sender: TField; var Text: string;
      DisplayText: Boolean);
    procedure OnGetText_Agg2(Sender: TField; var Text: string;
      DisplayText: Boolean);
  public
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  { 关联数据控件 }
  DBGrid1.DataSource := DataSource1;
  DataSource1.DataSet := ClientDataSet1;

  { 先打开前面例子中留下的测试文件 }
  ClientDataSet1.LoadFromFile('C:\Temp\Test.xml');

  { 添加索引, 其中分组级别是 2 }
  ClientDataSet1.AddIndex('Index1', '班级;年龄', [], '', '', 2);
  { 给数据集指定此索引 }
  ClientDataSet1.IndexName := 'Index1';

  { 数据结构变化时一般需要先关闭数据集 }
  ClientDataSet1.Close;

  { 添加统计字段 Agg1: 按班分组统计语文总成绩 }
  with TAggregateField.Create(Self) do begin
    FieldName := 'Agg1';
    Expression := 'Sum(语文成绩)';
    IndexName := 'Index1';
    GroupingLevel := 1;
    Active := True;
    OnGetText := OnGetText_Agg1;
    DataSet := ClientDataSet1;
  end;
  { 添加统计字段 Agg2: 各班分别按年龄分组统计语文总成绩 }
  with TAggregateField.Create(Self) do begin
    FieldName := 'Agg2';
    Expression := 'Sum(语文成绩)';
    IndexName := 'Index1';
    GroupingLevel := 2;
    Active := True;
    OnGetText := OnGetText_Agg2;
    DataSet := ClientDataSet1;
  end;

  { 需要在 DBGrid 中显示的字段 }
  with DBGrid1.Columns do begin
    Add.FieldName := '班级';
    Add.FieldName := '姓名';
    Add.FieldName := '年龄';
    Add.FieldName := '语文成绩';
    Add.FieldName := 'Agg1';
    Add.FieldName := 'Agg2';
  end;

  { 打开数据集并激活统计 }
  ClientDataSet1.Open;
  ClientDataSet1.AggregatesActive := True;
end;

procedure TForm1.OnGetText_Agg1(Sender: TField; var Text: string; DisplayText: Boolean);
begin
  if gbLast in ClientDataSet1.GetGroupState(1) then
    Text := Sender.AsString else Text := '';
end;

procedure TForm1.OnGetText_Agg2(Sender: TField; var Text: string; DisplayText: Boolean);
begin
  if gbLast in ClientDataSet1.GetGroupState(2) then
    Text := Sender.AsString else Text := '';
end;

end.