来自delphi的Access db中的多个INNER JOINS

Question

我编写了最简单的程序，连接到 accessessdb 并从 Memo 列执行 SQL 查询。

查询示例：

SELECT 
    company_name, date_of_order_start, date_of_order_finish
FROM 
    customers
INNER JOIN 
    orders ON customers.id_customer = orders.id_customer
WHERE 
    company_name='Ампер';

它工作正常，但是这个查询

SELECT 
    company_name, date_of_order_start, date_of_order_finish, amount
FROM 
    customers
INNER JOIN 
    orders ON customers.id_customer = orders.id_customer
INNER JOIN 
    invoice ON invoice.id_order = orders.id_order
WHERE 
    company_name='Ампер';

返回语法错误

表达式“customers.id_customer=orders.id_customer”中缺少运算符 INNER JOIN invoice ON invoice.id_order=orders.id_orde' 。

是的，.id_order 中的最后一个 r 没有显示。

请帮忙，我哪里出错了。

程序代码下方

    unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Data.DB, Vcl.StdCtrls, Vcl.DBCtrls,
  Vcl.Grids, Vcl.DBGrids, Vcl.ExtCtrls, Data.Win.ADODB;

type
  TForm1 = class(TForm)
    ADOConnection1: TADOConnection;
    DataSource1: TDataSource;
    ADOQuery1: TADOQuery;
    Panel1: TPanel;
    DBGrid1: TDBGrid;
    DBNavigator1: TDBNavigator;
    Button1: TButton;
    Button2: TButton;
    Memo1: TMemo;
    Label1: TLabel;
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Memo1Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
//проверим - есть ли текст в Memo. Если нет, выходим:
  if Memo1.Text = '' then begin
    ShowMessage('Вначале введите запрос!');
    Memo1.SetFocus;
    Exit;
  end;
  //текст есть. Очистим предыдущий запрос в наборе данных:
  ADOQuery1.SQL.Clear;
  //добавим новый запрос из Memo:
  ADOQuery1.SQL.Add(Memo1.Text);
  //открываем набор данных, т.е. выполняем запрос:
ADOQuery1.Open;

end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Memo1.Clear;
end;

procedure TForm1.Memo1Change(Sender: TObject);
begin
  ADOQuery1.SQL.Add(Memo1.Text);
  ADOQuery1.SQL := Memo1.Lines;
end;


end.

Answer 1

更多信息：这里将Memo1.Text 两次写入ADOQuery1.SQL

procedure TForm1.Memo1Change(Sender: TObject);
begin
  ADOQuery1.SQL.Add(Memo1.Text);       // <-- first time
  ADOQuery1.SQL := Memo1.Lines;        // <-- 2nd time
end;

您在此处将语句写入 ADOQuery1：

 //текст есть. Очистим предыдущий запрос в наборе данных:
  ADOQuery1.SQL.Clear;
  //добавим новый запрос из Memo:
  ADOQuery1.SQL.Add(Memo1.Text);

Answer 2

非常感谢所有试图帮助我的人！

in access db JOIN 必须在 ()，所以这个查询可以正常工作：

 SELECT 
company_name, date_of_order_start, date_of_order_finish, amount
    FROM 
(customers
    INNER JOIN orders ON customers.id_customer=orders.id_customer)
    INNER JOIN invoice ON invoice.id_order=orders.id_order
    WHERE company_name='Ампер';

Answer 3

我建议在您的查询周围添加错误处理：

Try
  ....
  // setup and execute your query

    except on e: exception do
      begin
        LogMyErrorSomehow(format('ERROR: [%s-%s] SQL:[%s]',
           [e.ClassType.ClassName, e.Message, ADOQuery1.SQL.text]));
      end;
    end;
end;