unit Unit6; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, LiteCall, LiteConsts, Vcl.StdCtrls, Data.DB, MemDS, DBAccess, LiteAccess; type TForm6 = class(TForm) LiteConnection1: TLiteConnection; LiteQuery1: TLiteQuery; Button1: TButton; LiteQuery2: TLiteQuery; Button2: TButton; procedure Button1Click(Sender: TObject); procedure Button2Click(Sender: TObject); private { Private declarations } public { Public declarations } end; var Form6: TForm6; implementation {$R *.dfm} procedure TForm6.Button1Click(Sender: TObject); begin LiteQuery1.Close; LiteQuery1.SQL.Text := 'SELECT MAX(age) AS max_age FROM max_test'; LiteQuery1.Open; if LiteQuery1.IsEmpty then begin ShowMessage('IsEmpty'); end else begin ShowMessage('非空'); ShowMessage(LiteQuery1.FieldByName('max_age').AsString); if LiteQuery1.FieldByName('max_age').IsNull then begin ShowMessage('为null'); end else begin ShowMessage(LiteQuery1.FieldByName('max_age').AsString); end; end; end; procedure TForm6.Button2Click(Sender: TObject); begin LiteQuery2.Close; LiteQuery2.SQL.Text := 'SELECT MAX(name) AS max_name FROM max_test'; LiteQuery2.Open; if LiteQuery2.IsEmpty then begin ShowMessage('IsEmpty'); end else begin ShowMessage('非空'); ShowMessage(LiteQuery2.FieldByName('max_name').AsString); if LiteQuery2.FieldByName('max_name').IsNull then begin ShowMessage('为null'); end else begin ShowMessage(LiteQuery2.FieldByName('max_name').AsString); end; end; end; end.