[英]Self-referential join, multiple rows
我有一個tbl:
| user | crs | status |
| usr1 | crs1 | stat1 |
| user1 | crs1 | stat2 |
| user2 | crs2 | stat1 |
我怎樣才能得到:
user | crs1.status | crs2.status?
我正在努力:
select distinct
mstr.[person username],
abt.[module name],
abt.[Lesson completion status],
eoc.[module name],
eoc.[Lesson completion status]
from
[aht16] as mstr
right join
[aht16] as abt on (mstr.[person username] = abt.[person username]
and abt.[module name] = 'sdfsdfsdfsfd)'
and abt.[Lesson completion status] = 'completed')
right join
[aht16] as EOC on (mstr.[person username] = EOC.[person username]
and eoc.[module name] = 'sdfsdfsdfs'
and eoc.[Lesson completion status] = 'completed')
where
mstr.[course title] = 'sdf'
一種方法是條件聚合:
select user,
max(case when crs = 'crs1' then status end) as crs1_status,
max(case when crs = 'crs2' then status end) as crs2_status
from aht16 as mstr
group by user;
注意:這使用表中描述的列名。 該查詢使用了一組不同的名稱。
簡單易用!
我以為自我加入會奏效,但只會增加行數。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.