mysql - 想在单行中获取重复的数据

Question

我想在一行中获取重复的行，下面是我的表格

每月出勤率

我的查询:

SELECT distinct a.* 
FROM monthly_attendance a 
WHERE a.month = 9
    AND a.year = 2018 
    AND a.batch in (5) 
    AND a.student_id=257

但是多行显示，下面是我的结果:

Answer 1

你应该使用(假的)聚合函数来减少行数

select student_id
    , batch
    , roll_no
    , month
    , year
    , min(a1)
    , min(a2)
    , min(a3)
    , min(a4)
    , min(a5)
    , min(a6)       
    , min(a7)
    , min(a8)
    , min(a9)
    , min(a10)
    , min(a11)
    , min(a12)      
    , min(a13)
    , min(a14)
    , min(a15)
    , min(a16)
    , min(a17)
    , min(a18)      
    , min(a19)  
from monthly_attendance a 
WHERE a.month = 9 
    AND a.year = 2018 
        AND a.batch in (5) 
            and a.student_id=257
GROUP BY student_id
    , batch
    , roll_no
    , month
    , year