这应该很容易。在MySQL中，我可以这样做：
select sum(column1*column2) as sum1 from table
你如何使用sqlite在Rails中执行此操作？我已经尝试了find_by_sql以及上面的确切查询，以及find（：all，：select =＆gt; ...）和各种其他事情，但没有返回正确的值。大多数都是空白的，如下：
[#<Element> ]
我可以循环，拉出值，然后求和，但这样做似乎很荒谬。
有人能指出我明显缺少的东西吗？谢谢！
答案 0 :(得分：3)
答案 1 :(得分：1)
正如@glortho在评论中所说，解决方案是
import 'package:auto_orientation/auto_orientation.dart';
import 'package:chewie/chewie.dart';
import 'package:chewie/src/chewie_player.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:video_player/video_player.dart';
void main() {
runApp(
ChewieDemo(),
);
}
class ChewieDemo extends StatefulWidget {
ChewieDemo({this.title = 'Chewie Demo'});
final String title;
@override
State<StatefulWidget> createState() {
return _ChewieDemoState();
}
}
class _ChewieDemoState extends State<ChewieDemo> {
TargetPlatform _platform;
VideoPlayerController _videoPlayerController1;
VideoPlayerController _videoPlayerController2;
ChewieController _chewieController;
@override
void initState() {
super.initState();
_videoPlayerController1 = VideoPlayerController.network(
'https://flutter.github.io/assets-for-api-docs/assets/videos/butterfly.mp4');
_videoPlayerController2 = VideoPlayerController.network(
'https://www.sample-videos.com/video123/mp4/480/big_buck_bunny_480p_20mb.mp4');
_chewieController = ChewieController(
videoPlayerController: _videoPlayerController1,
aspectRatio: 3 / 2,
autoPlay: true,
looping: true,
routePageBuilder: (BuildContext context, Animation<double> animation,
Animation<double> secondAnimation, provider) {
return AnimatedBuilder(
animation: animation,
builder: (BuildContext context, Widget child) {
return VideoScaffold(
child: Scaffold(
resizeToAvoidBottomPadding: false,
body: Container(
alignment: Alignment.center,
color: Colors.black,
child: provider,
),
),
);
},
);
}
// Try playing around with some of these other options:
// showControls: false,
// materialProgressColors: ChewieProgressColors(
// playedColor: Colors.red,
// handleColor: Colors.blue,
// backgroundColor: Colors.grey,
// bufferedColor: Colors.lightGreen,
// ),
// placeholder: Container(
// color: Colors.grey,
// ),
// autoInitialize: true,
);
}
@override
void dispose() {
_videoPlayerController1.dispose();
_videoPlayerController2.dispose();
_chewieController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
title: widget.title,
theme: ThemeData.light().copyWith(
platform: _platform ?? Theme.of(context).platform,
),
home: Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Column(
children: <Widget>[
Expanded(
child: Center(
child: Chewie(
controller: _chewieController,
),
),
),
FlatButton(
onPressed: () {
_chewieController.enterFullScreen();
},
child: Text('Fullscreen'),
),
Row(
children: <Widget>[
Expanded(
child: FlatButton(
onPressed: () {
setState(() {
_chewieController.dispose();
_videoPlayerController2.pause();
_videoPlayerController2.seekTo(Duration(seconds: 0));
_chewieController = ChewieController(
videoPlayerController: _videoPlayerController1,
aspectRatio: 3 / 2,
autoPlay: true,
looping: true,
);
});
},
child: Padding(
child: Text("Video 1"),
padding: EdgeInsets.symmetric(vertical: 16.0),
),
),
),
Expanded(
child: FlatButton(
onPressed: () {
setState(() {
_chewieController.dispose();
_videoPlayerController1.pause();
_videoPlayerController1.seekTo(Duration(seconds: 0));
_chewieController = ChewieController(
videoPlayerController: _videoPlayerController2,
aspectRatio: 3 / 2,
autoPlay: true,
looping: true,
);
});
},
child: Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Text("Video 2"),
),
),
)
],
),
Row(
children: <Widget>[
Expanded(
child: FlatButton(
onPressed: () {
setState(() {
_platform = TargetPlatform.android;
});
},
child: Padding(
child: Text("Android controls"),
padding: EdgeInsets.symmetric(vertical: 16.0),
),
),
),
Expanded(
child: FlatButton(
onPressed: () {
setState(() {
_platform = TargetPlatform.iOS;
});
},
child: Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Text("iOS controls"),
),
),
)
],
)
],
),
),
);
}
}
class VideoScaffold extends StatefulWidget {
const VideoScaffold({Key key, this.child}) : super(key: key);
final Widget child;
@override
State<StatefulWidget> createState() => _VideoScaffoldState();
}
class _VideoScaffoldState extends State<VideoScaffold> {
@override
void initState() {
SystemChrome.setPreferredOrientations([
DeviceOrientation.landscapeRight,
DeviceOrientation.landscapeLeft,
]);
AutoOrientation.landscapeAutoMode();
super.initState();
}
@override
dispose() {
SystemChrome.setPreferredOrientations([
DeviceOrientation.portraitUp,
DeviceOrientation.portraitDown,
]);
AutoOrientation.portraitAutoMode();
super.dispose();
}
@override
Widget build(BuildContext context) {
return widget.child;
}
}
这甚至适用于多个表
Element.sum( "column1*column2" )
SQL难以置信！