this is my mysql db schema:
I would like to create query that would return data about all trainings in a following way :
training.*, [type.type], [voivodeship.name] if there would be no type or voivodeship related to given training it should return null in the column value.
For example:
{
"id": 1,
"name": "Example training 2",
"description": "This is a description 2",
"status": "status 2",
"registerFrom": null,
"registerTo": null,
"DateOfInsert": "2018-02-06T12:00:57.000Z",
"training types": "Example type 1,Example type 3,Example type 2"
"localizations": "loc 1, loc 3"
},
...
{
"id": 99,
"name": "Example training 99",
"description": "This is a description 99",
"status": "status 2",
"registerFrom": null,
"registerTo": null,
"DateOfInsert": "2018-02-06T12:00:57.000Z",
"training types": null,
"localizations": null
},
{
"id": 99,
"name": "Example training 99",
"description": "This is a description 99",
"status": "status 2",
"registerFrom": null,
"registerTo": null,
"DateOfInsert": "2018-02-06T12:00:57.000Z",
"training types": "Example type 9,Example type 4,Example type 2",
"localizations": "loc 56, loc 32"
},
this is my current query that returns trainings with information about its localizations (sadly it doesnt return the ones without them) and i also dont have idea how to modify it to return also all types:
SELECT `training`.*, GROUP_CONCAT(`voivodeship`.`name`) AS `Localizations`
FROM `training_localization`
INNER JOIN `training` ON (`training_localization`.`training_id` = `training`.`id`)
INNER JOIN `voivodeship` ON (`training_localization`.`voivodeship_id` = `voivodeship`.`id`)
GROUP BY `training`.`id`
I am not very experienced with sql. Is it even possible with one query?
According to Gordon answer i made new query, at it seems like it's working :):
SELECT t.*, GROUP_CONCAT(vs.name) AS Localizations, tw.types AS types
FROM training t
LEFT JOIN training_localization tl ON tl.training_id = t.id
LEFT JOIN voivodeship vs ON tl.voivodeship_id = vs.id
LEFT JOIN(
SELECT t.*, GROUP_CONCAT(ty.type) AS Types
FROM training t
LEFT JOIN training_type tt ON tt.training_id = t.id
LEFT JOIN type ty ON tt.type_id = ty.id
GROUP BY t.id
) tw ON tw.id = t.id
GROUP BY t.id;
If you want all of something, think "outer join". If you want all trainings, that should be the first table in a series of left join
s:
SELECT t.*, GROUP_CONCAT(vs.name) AS Localizations
FROM training t LEFT JOIN
training_localization tl
ON tl.training_id = t.id LEFT JOIN
voivodeship vs
ON tl.voivodeship_id = vs.id
GROUP BY t.id;
Notes:
LEFT JOIN
s keep everything in the first table and matching rows in the subsequent tables (unless you undo it with an inner join or where clause).
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