ADO多線程數(shù)據(jù)庫查詢通常會出現(xiàn)3個(gè)問題：

1、CoInitialize 沒有調(diào)用 （CoInitialize was not called）；所以，在使用任何dbGo對象前，必須手 調(diào)用CoInitialize和CoUninitialize。調(diào)用CoInitialize失敗會產(chǎn)生"CoInitialize was not called"例外。

2、畫布不允許繪畫 （Canvas does not allow drawing）；所以，必須通過Synchronize過程來通知主線程訪問主窗體上的任何控件。

3、不能使用主ADO連接 （Main TADoConnection cannot be used!）；所以，線程中不能使用主線程中TADOConnection對象，每個(gè)線程必須創(chuàng)建自己的數(shù)據(jù)庫連接。

     Delphi2007安裝后在X:/Program Files/Common Files/CodeGear Shared/Data目錄下有一個(gè)dbdemos.mdb文件，用來作為測試的例子。dbdemos.mdb中的customer表保存了客戶信 息，orders表中保存了訂單信息。

       測試程序流程大致是這樣的：在主窗體上放TADOConnection和TQuery控件，啟動時(shí)這個(gè)TQuery從Customer表中查出客戶編碼 CustNo和公司名稱Company，放到三個(gè)Combox框中，分別在三個(gè)列表框中選定客戶公司名稱，按照公司名稱所對應(yīng)的客戶代碼建立三個(gè)線程同時(shí) 在orders表中查詢銷售日期SaleDate分別填入ListBox中

unit
 Main;

interface

uses
  Windows,  Messages,  SysUtils,   Variants, Classes, Graphics,   Controls, Forms,   Dialogs,
 DB,       ADODB,      StdCtrls;

type
  TForm2 =class (TForm)
    ComboBox1:  TComboBox;
    ComboBox2:  TComboBox;
    ComboBox3:   TComboBox;
    ListBox1:    TListBox;
    ListBox2:   TListBox;
    ListBox3:    TListBox;
    Button1:  TButton;
    ADOConnection1:  TADOConnection;
    ADOQuery1:  TADOQuery;
    Label1: TLabel;
    Label2:  TLabel;
    Label3: TLabel;

    procedure  FormCreate(Sender: TObject) ;
    procedure  Button1Click(Sender: TObject) ;
  private
    { Private declarations }
  public
    { Public declarations }
  end    ;
var
  Form2:    TForm2;
implementation

uses
 ADOThread;

{$R *.dfm}

procedure   TForm2.Button1Click(Sender: TObject);
const
  SQL_CONST= 'Select SaleDate from orders where CustNo = %d' ;
var
  c1,c2,c3: Integer  ;
  s1, s2,s3: string ;
begin

  //取得三個(gè)選擇框客戶的編碼

  c1:= Integer(ComboBox1.Items.Objects[ComboBox1.ItemIndex]);
  c2:= Integer(ComboBox2.Items.Objects[ComboBox2.ItemIndex]);
  c3:= Integer(ComboBox3.Items.Objects[ComboBox3.ItemIndex]);
  //生成SQL 查詢語句
  s1:=Format(SQL_CONST,[c1]);
  s2:=Format(SQL_CONST,[c2]);
  s3:=Format(SQL_CONST,[c3]);
  //三個(gè)線程同時(shí)查詢
  TADOThread.Create(s1,ListBox1,Label1) ;
  TADOThread.Create(s2,ListBox2,Label2);
  TADOThread.Create(s3,ListBox3,Label3);
end ;

procedure TForm2.FormCreate(Sender: TObject);
var
  strSQL:string ;
begin
  strSQL:='SELECT CustNo,Company FROM customer';
  ADOQuery1.Close;
  ADOQuery1.SQL.Clear;
  ADOQuery1.SQL.Add(strSQL);
  ADOQuery1.Open;
  ComboBox1.Clear;
  ComboBox2.Clear;
  ComboBox3.Clear;
  //將客戶Company和相關(guān)CustNo填到ComboBox中
  while  not  ADOQuery1.Eof  do
  begin
    ComboBox1.AddItem(ADOQuery1.Fields[1].asString, TObject(ADOQuery1.Fields[0].AsInteger));
    ADOQuery1.Next;
  end ;
  ComboBox2.Items.Assign(ComboBox1.Items);
  ComboBox3.Items.Assign(ComboBox1.Items);
  // 默認(rèn)選中第一個(gè)
  ComboBox1.ItemIndex := 0;
  ComboBox2.ItemIndex := 0;
  ComboBox3.ItemIndex := 0;
end ;

end.
{ADO查詢多線程單元}


unit
 ADOThread;

interface

uses
  Classes,StdCtrls,ADODB;
type
  TADOThread = class(TThread)
  private
    { Private declarations }
    FListBox:TListBox;
    FLabel:TLabel;
    ConnString:WideString;
    FSQLString:string;
    procedure  UpdateCount;
  protected
    procedure  Execute; override;
  public
    constructor  Create(SQL:string;LB:TListBox;Lab:TLabel);
  end   ;

implementation

uses  Main,SysUtils,ActiveX;

{ TADOThread }

constructor  TADOThread.Create(SQL: string; LB: TListBox;Lab:TLabel);
begin
  ConnString:=Form2.ADOConnection1.ConnectionString;
  FListBox:=LB;
    FLabel:=Lab;
  FSQLString:=SQL;
  Inherited  Create(False);
end  ;

procedure  TADOThread.Execute;
var
  Qry:TADOQuery;
  i:Integer;
begin
  { Place thread code here }
  FreeOnTerminate:=True;
  CoInitialize(nil);
    //必須調(diào)用（需Uses ActiveX）
  Qry:=TADOQuery.Create(nil);
  try
    Qry.ConnectionString:=ConnString;   //必須有自己的連接
    Qry.Close;
    Qry.SQL.Clear;
    Qry.SQL.Add(FSQLString);
    Qry.Open;
    FListBox.Clear;
    for  i := 0 to 100 do     //為了執(zhí)行久點(diǎn)重復(fù)歷遍數(shù)據(jù)集101次
      begin
        while  not Qry.Eof And  not Terminated do
        begin
        FListBox.AddItem(Qry.Fields[0].asstring,nil);
          //如果不調(diào)用Synchronize，會出現(xiàn)Canvas Does NOT Allow Drawing
          Synchronize(UpdateCount);
          Qry.Next;
        end ;
        Qry.First;
        FListBox.AddItem('*******',nil);
      end ;
  finally
    Qry.Free;
  end ;
  CoUninitialize;
end  ;

procedure   TADOThread.UpdateCount;
begin
  FLabel.Caption:=IntToStr(FListBox.Items.Count);
end     ;

end.