显示问题

Question

你好我有我想要显示从每个部分各自的候选人只有第一个问题学生数据...

Answer 1

解决方案模仿SQL SERVER Row_Number（）函数。谷歌MySQL的顺序点在正确的方向。

/*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，你要为每一个部分的第一个3个问题，但你没有考虑部分在你的查询中。以下查询将完成这项工作。

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