Question

我有一个评估结果数据库，其中包含识别学生，年级，年份和学期的字段。下面的查询找到了在某个起点和终点对特定主题进行评估的学生：

SELECT
  a1.PupilId
FROM assessment as a1
  JOIN assessment as a2
    USING (PupilId)
WHERE a1.GradeID in('1A','1B','1C')
    AND a2.GradeID in('5A','5B','5C')
    AND a1.NCYear = '1'
    AND a1.Term = '6'
    AND a2.NCYear = '2'
    AND a2.Term = '6'
    AND a1.Subject = '31'
    AND a2.Subject = '31'
    AND a1.Type = 'assessment'
    AND a2.Type = 'assessment'

这种方法很好，但现在我想找到具有起始等级的学生（即NCYear ='1'和Term ='6'），但没有最终成绩的条目。我玩过NOT EXISTS，但无法让它工作。

澄清一下，这是评估表：

id | Subject | PupilId | NCYear | Term | GradeID | Type
--------------------------------------------------------
1  | 31      | 1       | 1      | 6    | 1A      | assessment
2  | 31      | 1       | 2      | 6    | 5A      | assessment
3  | 31      | 2       | 1      | 6    | 1A      | assessment

上面的SQL查询应该返回PupilID 1.我需要返回PupilID 2的查询，开始评估在那里，但没有结束。

有什么建议吗？

Answer 1

使用if

尝试此查询

SELECT
  a1.PupilId
FROM assessment as a1
  JOIN assessment as a2
    USING (PupilId)
WHERE a1.GradeID in('1A','1B','1C')
    AND a2.GradeID in('5A','5B','5C')
    AND a1.NCYear = '1'
    AND a1.Term = '6'
    AND a2.NCYear = '2'
    AND a2.Term = '6'
    AND a1.Subject = '31'
    AND a2.Subject = '31'
    AND a1.Type = 'assessment'
    AND a2.Type = 'assessment'
    AND IF(a1.NCYear = 1, IF(a1.Term = 6,a2.GradeID IS NULL,1),1)

Answer 2

您需要使用OUTER JOIN：

SELECT
  a1.PupilId
FROM assessment as a1
  OUTER JOIN assessment as a2
    ON a2.PupilId = a2.PupilId AND a2.NCYear = '2' AND a2.GradeID in('5A','5B','5C') AND a2.Term = '6' AND a2.Subject = '31' AND a2.Type = 'assessment'        
WHERE a1.GradeID in('1A','1B','1C')
    AND a1.NCYear = '1'
    AND a1.Term = '6'
    AND a1.Subject = '31'
    AND a1.Type = 'assessment'
    AND a2.PupilId IS NULL

查找匹配一组条件而另一组条件不匹配的记录

2 个答案: