Question

你好我有学生数据我想只显示每个部分各候选人的第一个问题......

Answer 1

解决方案模仿SQL SERVER Row_Number（）函数。谷歌mysql按顺序在点上方向正确。

/*create temporary table t(can_id int,    status varchar(20));

insert into t values            
(001 ,   'section 1 question 1'),    
(001 ,   'section 1 question 2'),   
(001 ,   'section 1 question 3'),  
(001 ,   'section 1 question 4'),    
(001 ,   'section 2 question 1'),    
(001 ,   'section 2 question 2'),    
(001 ,   'section 2 question 3'),    
(001 ,   'section 2 question 4'),    
(001 ,   'section 3 question 1'),    
(001 ,   'section 3 question 2'),    
(001 ,   'section 3 question 3'),    
(002 ,   'section 1 question 1'),
(002 ,   'section 1 question 2'),
(002 ,   'section 1 question 3'),
(002 ,   'section 2 question 1'),
(002 ,   'section 2 question 2'),
(002 ,   'section 2 question 3'),
(002 ,   'section 3 question 1'),
(002 ,   'section 3 question 2'),
(002 ,   'section 3 question 3'),
(002 ,   'section 3 question 4');

*/

select s.tcanid as 'can.id', substring(s.tstatus,11,11) as Question
from
(
select   t.can_id as tcanid, t.status as tstatus ,
            @sno :=if(@previd = concat(t.can_id,substring(t.status,1,9)),@sno + 1,1) as canid
          ,@previd:=concat(t.can_id,substring(t.status,1,9)) prevcanid
from t,
(select @sno:= 0) as sn
,(select @Previd:= '') as p
) s
where s.canid <= 3

Answer 2

根据您的要求，您希望每个部分都有前3个问题，但您没有考虑查询中的部分。以下查询将执行此作业。

SELECT data_set.* 
FROM
(

    SELECT  temp.can_id
            , temp.Section
            , temp.Question
            , ROW_NUMBER() OVER (PARTITION BY temp.can_id,temp.Section ORDER BY temp.can.id,temp.Section) as QUESTION_NO
    FROM 
    (
        SELECT  can.id as can_id
                , SUBSTRING(status,11,11) as Question
                , SUBSTRING(status,1,9) as Section
        FROM samp_dat
    ) temp
) data_set
WHERE 
    data_set.QUESTION_NO <=3

显示问题

2 个答案: