动态创建TDATABASE后连接至数据库，为什么提示duplicate database name 'ZB'


代码如下,buttonclick(sender:tobject);
var 
  database:tdatabase;
  query:tquery;
  datasource:tdatasource;
begin 
 database:=tdatabase.Create(nil);
 with database do
    begin
      Connected:=false;
      Params.Clear;
      Params.Values['user name']:='sa';
      params.Values['password']:='limison';
      LoginPrompt:=false;
      databasename:='ZB';
    end;
try
      database.Connected:=true;
      datasource:=TDataSource.create(nil);
      query:=TQuery.Create(nil);
      query.DatabaseName:='ZB';
      datasource.DataSet:=query;
      .............
except
end;
end;点击一次BUTTON后,执行成功,再点一次就会出现提示:duplicate database name 'ZB'