按学生名称获取列名

Question

是否可以在查询中获取表的列名？我正在使用PDO

stu_name  maths science music art 

John   done  done  - done 
Max    -  done  - done 
Peter   -  done  -  - 

E.g.我如何获得John尚未完成的科目（-）？ music应该是结果。

这就是我现在所在的地方。我不知道怎么做。

$sql = "SELECT * FROM coll_student WHERE stu_name = :name AND ?? = '-' LIMIT 1"; 
$stat = $connect->prepare($sql); 
$stat->execute(array(':name'=>"John")); 
$output = $stat->fetchAll(PDO::FETCH_COLUMN); 

Answer 1

你可以这样做：

SELECT 
    GROUP_concat(COALESCE(CASE WHEN maths = '-' THEN 'maths' END, ''), 
       COALESCE(CASE WHEN science = '-' THEN 'science' END, ''), 
       COALESCE(CASE WHEN art  = '-' THEN 'art'  END, ''), 
       COALESCE(CASE WHEN music = '-' THEN 'music' END, '')) AS SubjectsNotDone 
FROM coll_student 
WHERE stu_name = 'John' 
AND ((maths = '-') OR 
     (science = '-') OR 
     (art  = '-') OR 
     (music = '-')) ; 

这会给你：

| SubjectsNotDone | 
|-----------------| 
|   music | 

• SQL Fiddle Demo

---

但是，您的表格不是normalized。你可以把它简单，更容易，更在性能方面，通过创建一个新的表Subjects：

• SubjectId，
• SubjectName。

然后，表coll_student将是这样的：

• stu_name，

• SubjectId - Foreign key给受检者表：

  constraint FK_SubjectId foreign key (SubjectId) references Subjects(SubjectId) 
  

• Status：位或INT作为标志完成与否（或其他状态，如果你有）。

那么您的查询就会简单得多，这样的事情：

SELECT subjectname 
FROM coll_student AS c 
INNER JOIN Subjects AS s ON c.SubjectID = s.SubjectId 
WHERE c.name = 'John' AND c.Status = 0; 

• Updated SQL Fiddle Demo with the new design