Create a view to show average over a set
I have a table,
tbl_courses
------------
int id //pk
int id_formation //fk
int credits
enum lang // en, fr, etc
The data in the table looks like this
id | id_formation | credits | lang
1 | 101 | 4 | en
2 | 101 | 6 | en
3 | 101 | 5 | fr
4 | 102 | 8 | en
5 | 102 | 2 | fr
6 | 103 | 3 | fr
I want to have a view that shows the per开发者_如何学编程centage of lang-credits for each id_formation
, something like
id_formation | en_percent | fr_percent
101 | 66 | 33
102 | 80 | 20
103 | 0 | 100
I managed to make a query to do this, but mysql won't let me make a view out of it
SELECT
a.id_formation,
en_percent
//fr_percent
FROM tbl_courses a
JOIN (
SELECT
a.id_formation,
FORMAT(SUM(a.credits)*100/b.total,0) AS 'en_percent'
FROM tbl_courses a
LEFT JOIN (
SELECT id_formation, SUM(credits) as total
FROM tbl_courses
GROUP BY id_formation) AS b ON b.id_formation = a.id_formation
GROUP BY a.id_formation, a.lang HAVING a.lang='en'
) AS en ON en.id_formation=a.id_formation
//repeat join code and switch en to fr
GROUP BY id_formation
I repeat the code in the JOIN to get the fr_percent
. Is there a way to write this to make it view friendly?
I create a small test case with three languages. Look at the last query. Does it give you what you need? If so, I can probably help you create the view you want.
create table tbl_courses as
select 1 as id_formation, 'en' as lang, 25 as credits union all
select 1 as id_formation, 'fr' as lang, 50 as credits union all
select 1 as id_formation, 'sv' as lang, 25 as credits union all
select 2 as id_formation, 'en' as lang, 80 as credits union all
select 2 as id_formation, 'fr' as lang, 15 as credits union all
select 2 as id_formation, 'sv' as lang, 5 as credits;
alter table tbl_courses add primary key(id_formation, lang);
select id_formation
,count(*) as num_languages
,sum(credits) as total_credits
,sum(case when lang = 'en' then credits else 0 end) as en_creds
,sum(case when lang = 'fr' then credits else 0 end) as fr_creds
from tbl_courses
group
by id_formation;
+--------------+---------------+---------------+----------+----------+
| id_formation | num_languages | total_credits | en_creds | fr_creds |
+--------------+---------------+---------------+----------+----------+
| 1 | 3 | 100 | 25 | 50 |
| 2 | 3 | 100 | 80 | 15 |
+--------------+---------------+---------------+----------+----------+
2 rows in set (0.00 sec)
Thanks to Ronnis, the trick is sum(case when):
SELECT
id_formation,
FORMAT(sum(case when lang = 'en' then credits else 0 end)*100 / SUM(credits),0) as en_percent,
FORMAT(sum(case when lang = 'fr' then credits else 0 end)*100 / SUM(credits),0) as fr_percent
FROM
tbl_courses
GROUP BY id_formation
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