自與條件接合表

Question

我有以下類型的表：

表dummy1：

e_n t_s item 
a  t1 c 
a  t2 c 
a  t3 c 
a  t4 c 
b  p1 c 
b  p2 c 
b  p3 c 
b  p4 c 

T1，T2，T3，T4，P1，P2，P3，P4是時間戳在升序。 t1，t2，t3，t4是event_name'a'的升序時間戳。 p1，p2，p3，p4是event_name'b'升序的時間戳。

c是發生這些事件'a'和'b'的item_number。

我試圖寫它的結果應該是作爲查詢如下：

e_n1 e_n2 item t_s_1 t_s_2 
a  b  c  t1 p1 
a  b  c  t2 p2 
a  b  c  t3 p3 
a  b  c  t4 p4 

我曾嘗試下面的代碼：

select l.e_n as e_n_1, m.e_n as e_n_2, l.item, l.t_s as t_s_a, 
m.t_s as t_s_b from (
(select * from dummy where e_n = 'a') l 
join 
(select * from dummy where e_n = 'b') m 
on l.item = m.item and l.t_s < m.t_s 

的加入l.item = m.item需要，因爲有許多其他項目C1，C2，C3具有相同的結構

結果是：

e_n1 e_n2 item t_s_a t_s_b 
    a  b  c  t1 p1 
    a  b  c  t1 p2 
    a  b  c  t1 p3 
    a  b  c  t1 p4 
    a  b  c  t2 p1 
    a  b  c  t2 p2 
    a  b  c  t2 p3 

so on 

我如何以高效的方式實現我的結果？

Answer 1

select  min (case when e_n = 'a' then 'a' end) as e_n1 
      ,min (case when e_n = 'b' then 'b' end) as e_n2 
      ,item 
      ,min (case when e_n = 'a' then t_s end) as t_s_1 
      ,min (case when e_n = 'b' then t_s end) as t_s_2 

from  (select  d.* 
         ,row_number() over (partition by item,e_n order by t_s) as rn 

      from  dummy as d 
      ) d 

group by item 
      ,rn 

---

+------+------+------+-------+-------+ 
| e_n1 | e_n2 | item | t_s_1 | t_s_2 | 
+------+------+------+-------+-------+ 
| a | b | c | t1 | p1 | 
| a | b | c | t2 | p2 | 
| a | b | c | t3 | p3 | 
| a | b | c | t4 | p4 | 
+------+------+------+-------+-------+ 

Answer 2

首先，排序時間戳每一個事件，然後加入對排序表中的行數。

請嘗試下面的代碼。

select l.e_n as e_n_1, m.e_n as e_n_2, isnull(l.item,m.item) as item, l.t_s as t_s_a, 
    m.t_s as t_s_b from 
    (select *,(row_number() over (order by t_s)) as rn from dummy where e_n = 'a') l 
    full join 
    (select *,(row_number() over (order by t_s)) as rn from dummy where e_n = 'b') m 
    on l.item = m.item and l.rn=m.rn