MySql scoping problem with correlated subqueries
I'm having this Mysql query, It works:
SELECT
nom
,prenom
,(SELECT GROUP_CONCAT(category_en) FROM
(SELECT DISTINCT category_en FROM categories c WHERE id IN
(SELECT DISTINCT category_id FROM m3allems_to_categories m2c WHERE m3allem_id = 37)
) cS
) categories
,(SELECT GROUP_CONCAT(area_en) FROM
(SELECT DISTINCT area_en FROM areas c WHERE id IN
(SELECT DISTINCT area_id FROM m3allems_to_areas m2a WHERE m3allem_id = 37)
) aSq
) areas
FROM m3allems m
WHERE m.id = 37
The result is:
nom prenom categories areas
Man Multi Carpentry,Paint,Walls Beirut,Baalbak,Saida
It works correclty, but only when i hardcode into the query the id that I want (37). I want it to work for all entries in the m3allem table, so I try this:
SELECT
nom
,prenom
,(SELECT GROUP_CONCAT(category_en) FROM
(SELECT DISTINCT category_en FROM categories c WHERE id IN
(SELECT DISTINCT category_id FROM m3allems_to_categories m2c WHERE m3allem_id = m.id)
) cS
) categories
,(SELECT GROUP_CONCAT(area_en) FROM
(SELECT DISTINCT area_en FROM areas c WHERE id IN
(SELECT DISTINCT area_id FROM m3allems_to_areas m2a WHERE m3allem_id = m.id)
) aSq
) areas
FROM m3allems m
And I get an error:
Unknown column 'm.id' in 'where clause'
Why? From the MySql manual:
13.2.8.7. Correlated Subqueries
[...]
Scoping rule: MySQL evaluates from inside to outside.
So... do this not work when the subquery is in a SELECT section? I did not read anything about that.
Does anyone know? What should I do? It took me a long time to build this query... I know it's a monster query but i开发者_如何学运维t gets what I want in a single query, and I am so close to getting it to work!
Can anyone help?
You can only correlate one level deep.
Use:
SELECT m.nom,
m.prenom,
x.categories,
y.areas
FROM m3allens m
LEFT JOIN (SELECT m2c.m3allem_id,
GROUP_CONCAT(DISTINCT c.category_en) AS categories
FROM CATEGORIES c
JOIN m3allems_to_categories m2c ON m2c.category_id = c.id
GROUP BY m2c.m3allem_id) x ON x.m3allem_id = m.id
LEFT JOIN (SELECT m2a.m3allem_id,
GROUP_CONCAT(DISTINCT a.area_en) AS areas
FROM AREAS a
JOIN m3allems_to_areas m2a ON m2a.area_id = a.id
GROUP BY m2a.m3allem_id) y ON y.m3allem_id = m.id
WHERE m.id = ?
The reason for the error is that in the subquery m
is not defined. It is defined later in the outer query.
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