Php 显示组concat的重复结果

我有这个疑问

SELECT users.*, student_subject.*, GROUP_CONCAT(written.score separator ' - ') as Wscore,SUM(written.score) as total, SUM(written.item) as item 

FROM users 
          JOIN written 
             ON 
                users.idnumber=written.idnumber 
          JOIN student_subject 
            ON 
                written.idnumber=student_subject.idnumber 

WHERE student_subject.teacher='$login_session' 
      AND written.section='$section' 
      AND written.level='$level' 
      AND written.year='$year' 
      AND written.subject='$subject' 
      AND users.gender='male' 
      AND written.period='first' 

GROUP BY written.idnumber order by users.lname

问题是组concat的结果显示重复的结果

例4-4-5-7-4-5

到

4-4-5-7-4-5-4-4-5-7-4-5-4-5-7-4-5-4-4-5-5-4-5-5-5-7-4-5

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如何删除这些重复项？

查看s.o.文章我以前尝试过使用distinct，但结果是4-5-7。。。应该是4-4-5-7-4-5你能创建一个