CODEWITHSUNDEEP
mysql
iWizard
iWizard

Reputation: 7094

How to multiple join tables?

I have 2 tables.

workers and experience

In table workers there is row worker_parent (because one worker can be responsible for other).

No I must connect tables like that:

SELECT w1.* FROM workers w1 LEFT JOIN workers w2 ON (w2.id = w1.worker_parent)

And that's ok. But I have to order by experience of w2 and I try to add table experience but it's connect to w1 and not to w2.

My question is how to add table experience (which has row worker_id) to w2 and order by experience AND SELECT data from w1.

This is my try.

SELECT w1.* FROM workers w1 LEFT JOIN workers w2 ON (w2.id = w1.worker_parent) LEFT JOIN experience e ON (w2.id = e.worker_id) ORDER BY e.experience DESC

Thank's for help

Upvotes: 1

Views: 66

Answers (1)

Puggan Se
Puggan Se

Reputation: 5846

if you only want child workers that have a parent with experince, you need to add a where (or change join type) (for readability i renamed w1 and w2 to w_child and w_parent)

SELECT w_child.*, e_parent.experience
FROM workers AS w_child 
LEFT JOIN workers AS w_parent ON (w_parent.id = w_child.worker_parent) 
LEFT JOIN experience AS e_parent ON (w_parent.id = e_parent.worker_id) 
WHERE e_parent.worker_id IS NOT NULL
ORDER BY e_parent.experience DESC

Upvotes: 1

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