顯示問題

Question

你好我有我想要顯示從每個部分各自的候選人只有第一個問題學生數據...

Answer 1

解決方案模仿SQL SERVER Row_Number（）函數。谷歌MySQL的順序點在正確的方向。

/*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

根據您的要求，你要爲每一個部分的第一個3個問題，但你沒有考慮部分在你的查詢中。以下查詢將完成這項工作。

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