Question

我有以下查询，其中的“ ID”字段不明确，我知道我需要使用别名，但是在第二个示例中使用别名时似乎做错了事

class SpecBuilder a b c where
  expectation :: a -> b -> SpecWith c
  specAll :: String -> [(a, b)] -> SpecWith c
  specAll name items = describe name $ mapM_ (uncurry expectation) items

我已遵循一些在线示例，并在第二行得到了一个错误。

 constructor(public navCtrl: NavController,private geolocation: Geolocation) { 

  navigator.geolocation.getCurrentPosition(this.onSuccess, this.onError);
    }
      onError(error) {
    alert('code: '    + error.code    + '\n' +
      'message: ' + error.message + '\n');
     }
     onSuccess(position) {
     let element = document.getElementById('map');
     element.innerHTML = 'Latitude: '  + position.coords.latitude      + '<br />' +
                  'Longitude: ' + position.coords.longitude     + '<br />' +
                  '<hr />'      + element.innerHTML;
                  console.log(element)
     }

请问有什么解决方法吗？

Answer 1

请尝试以下查询

SELECT t1.ID
FROM 01users AS t1
INNER JOIN 01modules ON 01modules.Modules_UserID = t1.ID 
INNER JOIN 01articles ON 01modules.ID = 01articles.ModuleID
WHERE User =  '$user' AND t1.ID = '$moduleid'
ORDER BY WeekID ASC

您还需要在where子句中使用别名。

此行

WHERE User =  '$user' AND ID = '$moduleid'

更改为此

WHERE User =  '$user' AND t1.ID = '$moduleid'

Answer 2

学习使用表别名！

SELECT *
FROM 01users u INNER JOIN
     01modules m
     ON m.Modules_UserID = u.ID INNER JOIN
     01articles a
     ON m.ID = 01artacles.ModuleID
WHERE u.User =  '$user' AND m.ID = '$moduleid'
ORDER BY ?.WeekID ASC

您应该对所有列引用进行限定，包括WeekId －这就是?的用途。

您还应该明确列出想要的列，而不要使用select *。

Answer 3

这是解决方案：

SELECT u.User, m.ID, a.Title, a.Topic, a.Text, a.WeekID, a.DatePosted, a.DateDue, a.TimePublished, a.File1, a.ID AS ArticleID
FROM 01users as u 
INNER JOIN 01modules AS m ON m.Modules_UserID = u.ID 
INNER JOIN 01articles AS a ON m.ID = a.ModuleID
WHERE User =  '$user' AND m.ID = '$moduleid'
ORDER BY WeekID ASC

具有内部联接的别名

3 个答案: