Question

通常我们从MySQL表中获取数据并逐行显示已获取的记录。但有时我们需要水平显示记录，如下所示。

Name * Student-ID * subject-1 * subject-2 * subject-3 * subject-4 * subject-5 ... So On
John      1            20           50          34          50         45 
Mercy     3            40           20          82          23         10
James     8            30           60          40          50         30
Agi       19           50           10          23          45         30

现在正在寻找能够产生上述结果的方法。下面是MySQL表格，我想提出上述预期结果。

表科目按类分类存储科目

subjectid
主旨名称
examinationid

表testinfo存储检查信息如下

assessment_id
idsubject

表考试将学生分数与相关信息一起存储

studentid
FNAME
L-NAME
id_subject
得分
- examinationid == assessment_id
- id_subject AND idsubject == subjectid

查询所有参加考试的学生（1）

SELECT *
FROM examinations AS exam
INNER JOIN examinfo AS info ON info.idsubject = exam.id_subject
WHERE info.assessment_id = 1

以上查询将生成结果垂直，以便如何水平转换或查询表格。我错过了它因为我之前从未以这种方式使用过SQL。谢谢你的手

Answer 1

您正在寻找MYSQL枢轴

STATIC WAY ：使用条件案例与分组

SELECT CONCAT(exam.fname," ",exam.lname) AS Name, exam.studentid, 
 SUM(CASE WHEN exam.id_subject = 1 THEN exam.score ELSE "NA" END) AS subject1,
 SUM(CASE WHEN exam.id_subject = 2 THEN exam.score ELSE "NA" END) AS subject2,  
 SUM(CASE WHEN exam.id_subject = 3 THEN exam.score ELSE "NA" END) AS subject3,
 SUM(CASE WHEN exam.id_subject = 4 THEN exam.score ELSE "NA" END) AS subject4,  
 SUM(CASE WHEN exam.id_subject = 5 THEN exam.score ELSE "NA" END) AS subject5
FROM examinations AS exam
INNER JOIN examinfo AS info ON info.idsubject = exam.id_subject
WHERE info.assessment_id = 1
GROUP BY exam.studentid

动态方式：GROUP_CONCAT使用CONCAT

SET @sql = NULL;
SELECT
    GROUP_CONCAT(DISTINCT 
    CONCAT('SUM(CASE WHEN id_subject= "', 
    id_subject, '" THEN score ELSE "NA" END) AS '
    , 'Subject-', id_subject))
INTO @sql
FROM
  examinations;

SET @sql = CONCAT('SELECT CONCAT(fname," ",lname) AS Name, 
                   studentid, ', @sql, ' 
                  FROM examinations
                  INNER JOIN examinfo AS info ON info.idsubject = id_subject
                  WHERE info.assessment_id = 1
                  GROUP BY studentid');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Answer 2

使用以下查询

SELECT CONCAT(exam.fname," ",exam.lname) AS Name, exam.studentid, 
 (CASE WHEN exam.subjectid = 1 THEN exam.score END ),
 (CASE WHEN exam.subjectid = 2 THEN exam.score END ),  
 (CASE WHEN exam.subjectid = 3 THEN exam.score END ),
 (CASE WHEN exam.subjectid = 4 THEN exam.score END ),  
 (CASE WHEN exam.subjectid = 5 THEN exam.score END ),
FROM examinations AS exam
INNER JOIN examinfo AS info ON info.idsubject = exam.id_subject
WHERE info.assessment_id = 1
GROUP BY exam.studentid

水平显示MySQL记录

2 个答案: