这个查询创建subject和examtypes的每个组合，然后使用一个右外连接来拉入在核心查询中看不到的组合。

SELECT
  coalesce(round((SUM(secured)/SUM(fullmark))*100), 0) as percent,
  all_subjects_examtypes.subject,
  all_subjects_examtypes.examtype
from
  tbl_marks
  right outer join (
    select distinct
      s.subject,
      e.examtype
    from
      tbl_marks as s
      cross join tbl_marks as e
  ) as all_subjects_examtypes on
    tbl_marks.subject = all_subjects_examtypes.subject and
    tbl_marks.examtype = all_subjects_examtypes.examtype
where
  all_subjects_examtypes.subject = 'MATHEMATICS'
group by
  all_subjects_examtypes.examtype

表中没有包含这些检查类型的记录，因此必须创建一个包含这些检查类型记录的记录集。
您可以通过交叉连接具有不同examtypes的不同主题来获得该记录集：

SELECT dsubject.subject, dexamptype.examtype
        FROM (SELECT DISTINCT subject FROM tbl_marks) dsubject,
            (SELECT DISTINCT examptype FROM tbl_marks) dexamptype

现在你有了一个关于每门学科和每种考试类型的记录
您可以在以下查询中使用它：

SELECT
    round((SUM(tbl_marks.`secured`)/SUM(tbl_marks.`fullmark`))*100) as percent
    subject_examtype.subject,
    subject_examtype.examtype   
FROM
    (
        SELECT dsubject.subject, dexamptype.examtype
        FROM (SELECT DISTINCT subject FROM tbl_marks WHERE subject = 'MATHEMATICS') dsubject,
            (SELECT DISTINCT examptype FROM tbl_marks) dexamptype
    ) subject_examtype
    LEFT OUTER JOIN tbl_marks 
        ON subject_examtype.subject = tbl_marks.subject
            AND subject_examptype.examtype = subject.examtype
GROUP BY subject_examtype.subject, subject_examtype.examtype;

因为这只是你想要的一个主题，所以这是一样的：

SELECT
    round((SUM(tbl_marks.`secured`)/SUM(tbl_marks.`fullmark`))*100) as percent
    subject_examtype.subject,
    subject_examtype.examtype   
FROM
    (SELECT DISTINCT 'MATHEMATICS' as subject, examtype FROM tbl_marks) subject_examtype
    LEFT OUTER JOIN tbl_marks 
        ON subject_examtype.subject = tbl_marks.subject
            AND subject_examptype.examtype = subject.examtype
GROUP BY subject_examtype.subject, subject_examtype.examtype;

但是如果您想对更多的主题执行此操作，那么查询的第一个版本就更有意义了。