Find leaf nodes in hierarchical tree

Your query didn't work because the sub-query includes NULL. The following slight modification works for me:

SELECT * FROM `mytree` WHERE `id` NOT IN (    SELECT DISTINCT `parentid` FROM `mytree` WHERE `parentid` IS NOT NULL)

sql database tree

No clue why your query didn't work. Here's the identical thing in left outer join syntax - try it this way?

select a.*from mytree a left outer join     mytree b on a.id = b.parentidwhere b.parentid is null

sql database tree

SELECT * FROM mytree AS t1LEFT JOIN mytree AS t2 ON t1.id=t2.parentidWHERE t2.parentid IS NULL

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