| [mySql] Retrieving columns without children
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fm86
msg:4314744 | 4:02 pm on May 19, 2011 (gmt 0) |
Hi everybody!
I am storing a tree in a mySql DB. Essentially I have 2 colums: id and parentId
For example:
id parentId
1 0 //root
2 1
3 1
4 2
5 3
Is there an efficient query to get only those rows that have no children (in this case row with ids 4 and 5)
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fm86
msg:4315143 | 8:16 am on May 20, 2011 (gmt 0) |
I tried
SELECT distinct t1.id FROM
clouds AS t1 LEFT JOIN clouds as t2
ON t1.id <> t2.parent
where clouds is the name of the table
but it returns all the rows... On the other way:
SELECT distinct t1.id FROM clouds AS t1 LEFT JOIN clouds as t2 ON t1.id = t2.parent
Returns the rows that are not leaves...
Any suggestion?
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coopster
msg:4316596 | 11:36 pm on May 23, 2011 (gmt 0) |
LEFT JOIN the alias where IS NULL.
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