MySQL记录在同一表中没有子

Question

I need to get the messages that are childless within the same table

ID  parent_id  body
1   NULL       my first comment (parent)
2   1          my reaction on first comment (child)
3   NULL       comment without reactions

As you can see the message are related my the parent_id. How can I get the parents without any child related. So me result would be

ID  parent_id  body
3   NULL       comment without reactions

I tried some stuff but I cant figure it out. Like select in select. On stackoverflow I could find some examples but does were mostly from 2 tables, not in the same. Maybe I mist does. Anyone can help me out?

Answer 1

Try using a NOT EXISTS clause which asserts that a given record has no parents and has no children:

SELECT *
FROM yourTable t1
WHERE
    t1.parent_id IS NULL AND
    NOT EXISTS (SELECT 1 FROM yourTable t2 WHERE t2.parent_id = t1.ID);

Answer 2

SELECT * FROM table1 WHERE parent_id IS NULL AND id NOT IN ( SELECT parent_id FROM table1 WHERE parent_id IS NOT NULL )