Sql server 在SQL Server中使用重复值联接3个表

我有三张桌子

存储主题及其详细信息的主题表

subject_id
subject_code
title
lec_units
lab_units
year_offered
course_offered
sem_offered

我存储学生注册科目的已注册表

id
course_code
student_id
subject_code
year_enrolled
school_year

最后是成绩表，我在其中存储每个科目的学生成绩

grade_id
student_id
subject_code
grade

我选择打印的等级如下：

Select g.subject_code,g.grade,su.title,su.year_offered,su.sem_offered,e.school_year from grades g left join subjects su on g.subject_code= su.subject_code left join enrolled e on g.subject_code = e.subject_code where (g.student_id='" + data_listview.FocusedItem.Text + "' and su.sem_offered = '1st' and e.year_enrolled= '1st')

但因为在我的注册表中，另一个学生也注册了同一科目，所以我得到了重复的行。那么，如何防止重复行？提前谢谢

试试这个

SELECT
  g.subject_code,
  g.grade,
  su.title,
  su.year_offered,
  su.sem_offered,
  e.school_year
FROM grades g
LEFT JOIN subjects su
  ON g.subject_code = su.subject_code
LEFT JOIN enrolled e
  ON g.subject_code = e.subject_code

  and g.student_id = e.student_id  -- you are missing this to link the student

WHERE (g.student_id = '" + data_listview.FocusedItem.Text + "'
AND su.sem_offered = '1st'
AND e.year_enrolled = '1st')

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您好，所以我尝试添加了您第一次评论的distinct，它很有效，尝试了这样做，也很有效，我更喜欢这个解决方案。谢谢你救了我的命！这是恰当的解决方案，而不是明显的欢呼。