与联接表的多对多关系

Question

I have 2 models with a many-to-many relationship, event and category . I am trying to put together a query which let's me get the events by the category name.

I have the following tables:

category

id | name

event

id | name

event_categories_join

category_id | event_id

I've successfully gotten the events from the category id by inner joining the pivot table.

SELECT * FROM event
INNER JOIN event_categories_join
ON event.id = event_categories_join.event_id
WHERE event_categories_join.category_id = 5

How do I do this by the name instead of the id?

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edit :

I three categories, Concert, Easter and Talks. I also an event, London Grammar which belongs to the categories Concert and Easter. Now I want to write a query where I provide the name of the category, and get the belonging events - in this case Concert.

Answer 1

You'll need another join. Try something like

SELECT * FROM event
INNER JOIN event_categories_join ON event.id = event_categories_join.event_id
INNER JOIN category ON category.id = event_categories_join.category_id
WHERE category.name = 'my_category';

As a side note: You should reconsider renaming event_categories_join to just event_categories . Or maybe event_categories_mapping . This is most probably more true to the domain in question, while the join naming is to tightly coupled with the fact we're dealing with a relational database.

Answer 2

SELECT temp.* FROM (
  SELECT event.id as eventid,event.name as eventName ,event_categories_join.* FROM event AS event 
INNER JOIN event_categories_join
ON event.eventid= event_categories_join.event_id 
) AS temp 
INNER JOIN category AS category ON 
category.id =temp.category_id
WHERE category.name = 'Maeh'