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List:       php-general
Subject:    Re: [PHP] Recursion with database tables
From:       David Otton <phpmail () jawbone ! freeserve ! co ! uk>
Date:       2003-02-19 13:42:42
[Download RAW message or body]

On Wed, 19 Feb 2003 14:16:47 +0000, you wrote:

>>Otherwise, yes, in MySQL you have to recurse down the tree deleting
>>comments.

>How would I go about recursing down the tree? Has anyone done this before?

I have, but it's been a while. Something like (pseudo-code) .

def delete_comments(a) :
    for b in a :
        c = "SELECT commentid FROM comments WHERE parentcommentid = a"
        if len(c) > 0 :
            delete_comments(c)
    "DELETE FROM comments WHERE commentid IN (a)"
    return

def main() :
    a = "SELECT commentid FROM comments WHERE topicid = 1234"
    delete_comments(a)
    "DELETE FROM topic WHERE topicid = 1234"

where a is a list of commentids, b is a single commentid and c is a list
of child commentids. This will delete the tree in a depth-first fashion.
This is quite an intensive way of doing things (potentially many selects
and deletes) but is just-about acceptable because you probably will
delete an entire topic so infrequently.

I recommend filling out the topicid on every post as the easier
solution, though.


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