按学生姓名获取列名称

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      -     -   

例如,如何获得John未完成的主题(-)？ music应该是结果.

这就是我现在所处的位置.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小提琴演示

但是,您的表未规范化.通过创建新表,您可以使其更简单,更容易,性能更高Subjects:

• SubjectId,
• SubjectName.

然后表格coll_student将是这样的:

• stu_name,

• SubjectId- 主题表的外键:

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

• Status:bit或int作为已完成或未完成的标志(如果有,则为其他状态).

然后你的查询会更简单,如下所示:

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;

• 使用新设计更新了SQL小提琴演示