Question

请有人告诉我，我做得不对。这是我想要执行的查询，但是当我运行命令时没有任何反应。我是SQL的新手，所以请原谅我的错误，如果有的话。

 SELECT  t.*,
 COUNT(DISTINCT t.subjects) AS subjectenrollment,
 u.urefnumber,
 u.uresidence
 FROM 
 (
  SELECT r.*,
  @curRank := IF( @prevRank = finalscore, @curRank, @incRank ) AS position,
  @incRank := @incRank + 1,
  @prevRank = finalscore
  FROM studentsreports r, 
  (
   SELECT @curRank := 0, 
   @prevRank = NULL, 
   @incRank := 1
  ) c
  ORDER BY finalscore ASC
 ) t LEFT JOIN studentstbl u ON t.studref = u.urefnumber
 WHERE t.author = :staff
 AND t.studentname = :student
 AND t.academicyr = :year
 AND t.academicterm = :term
 AND t.program = :program
 AND t.classes = :level
 AND t.subjects = :subject;

从代码中可以看出，我试图获取学生记录，并在每个科目中包含一个职位列，以及提供每个科目的学生人数。更重要的是，我想要包括每个学生的住宿状况，这也在不同的表格中。

在某一点上，我甚至想要添加他们累积的原始分数，即每个科目中获得的所有分数的总和，但我不知道如何使这成为可能。一位朋友已经建议在单独的查询中实现这一点，但不幸的是，我可以做得很好。拜托，我将非常感谢你的帮助。提前谢谢！

Answer 1

使用派生表和相关子查询来考虑此调整，而不需要@variables。下面的SQL语句处理以下列出的使用状态的以下需求：

每个主题的排名/排名列 - 顶级联合相关计数子查询
提供每个科目的学生人数 - 汇总计数派生表（内部联接条款）
每个学生的住宿状况 - 按字段分组（来自子句）
每个科目中所有分数的总和 - 总和派生表（来自条款）

SQL （带有绑定参数）

SELECT main.student_number, main.subjects, main.student_residence,
       main.accum_raw_scores, 
       (SELECT COUNT(*) 
        FROM (SELECT s.studref, s.subjects, SUM(s.finalscore) AS total_score
              FROM studentsreports s
              GROUP BY s.studref, s.subjects) AS sub
        WHERE sub.subjects = main.subjects
        AND sub.total_score >= main.accum_raw_scores) AS subject_rank,
       cnt.subject_student_count
FROM
  (SELECT r.studref AS student_number, r.subjects, u.uresidence AS student_residence, 
          SUM(r.finalscore) AS accum_raw_scores       
   FROM studentreports r
   LEFT JOIN studentstbl u ON r.studref = u.urefnumber
   WHERE r.author = :staff
   AND r.studentname = :student
   AND r.academicyr = :year
   AND r.academicterm = :term
   AND r.program = :program
   AND r.classes = :level
   AND r.subjects = :subject
   GROUP BY r.studref, r.subjects, u.uresidence) main
INNER JOIN 
   (SELECT sub.subjects, COUNT(*) AS subject_student_count 
    FROM studentreports sub 
    GROUP BY sub.subjects) cnt
ON cnt.subjects = main.subjects

无法使用Join执行SQL子查询

1 个答案: