Folder and subfolders: how to query?
i have got 2 tables which should show a folder structure as a tree. So every folder has an id and a name. if it is a subfolder of an other folder it开发者_JS百科 has an parent id like this:
Table folder:
Folderid name
11111112 xxy
11111113 yyy
11111114 yxy
...
table Structur
folderid parentid ...
11111112 NULL
11111113 11111112
11111114 11111113
My question now is how can i check with a mysql query whether a folder is a subfolder of another (but it hasnt to be the parent one)
For example:
How can i check whether folder 11111114
is in 11111112
???
I would check recursive but the problem is that the count is unkown so i downt now how often to do this step.
maybe u can help me??
The MySQL docs have some guidelines on storing hierarchical data: Managing Hierarchical Data in MySQL.
let's start with this structure (let's name table folders
). Maybe you can rework this case to yours.
{
id => 'int',
label => 'string', # folder name
parent => 'int' # reference to folder parent (only one)
# folder has unlimited number of children
}
some more pseudo-code
subtree_ids = select_subtree_ids (root)
if id_folder in subtree_ids
bingo! id_folder is subfolder of root
what you need is to write select_subtree_ids ()
you can't do this in one query (am I wrong?)
something like this (pseudo-code, again)
select_subtree (root) {
ids = (root); # result array contains initial id (for convenience)
while (TRUE) { # depth is unknown
# array of folder ids from next level only
my new_ids = sql_select_array ("SELECT id FROM folders WHERE parent IN (ids) AND id NOT IN (ids)");
break if no_new_ids;
ids = ids + new_ids;
}
return ids;
}
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