在mysql的同一张表上左联接

Question

I am trying to apply left join on same table but I am not getting the desired results.

I have this table

Table -- Pages

id    name        parent        status
1     AAA         0             draft
2     BBB         1             live
3     CCC         13            live
4     DDD         0             live
5     EEE         4             live
6     FFF         4             live

I want all the rows where id status is live and their parent id's status is also live.So in the above example id 2 should not appear as it's parent id 1 status is draft.

I have made a sqlfiddle -- http://www.sqlfiddle.com/#!2/d6b31/4

Any help is highly welcomed. Thanks in advance.

Answer 1

Make sure your fiddle's schema includes all cases. The cases you provided did not include a child not live without a parent.

This should do what you are expecting.

SELECT a.id, a.name, a.parent, a.status
FROM pages a
LEFT JOIN pages b ON a.parent = b.id and b.status='live'
WHERE a.status='live' AND (b.status='live' OR a.parent=0)

Adjusted cases:

(1, 'AAA', '0', 'draft'),
(2, 'BBB', '1', 'live'),
(3, 'CCC', '13', 'live'),
(4, 'DDD', '0', 'live'),
(5, 'EEE', '4', 'live'),
(6, 'FFF', '4', 'draft'),
(7, 'GGG', '0', 'draft')