I've searched the wiki and googled for "subselect" and "subquery", and not
found anything relevelant.
I'm evaluating whether CouchDB can handle an app which currently stores a tree
structure in a relational database using the "materialized path" represenation.
For example, the item with path "QG" is a child of the item with path "Q" and
a parent of the item with path "QGC".
The trickiest query is, in English, "find all items with work less than zero
and whether they have any children with work less than zero". The SQL for this
is
SELECT item.*, EXISTS (SELECT work FROM item AS d WHERE d.path > item.path AND
d.path <= item.path || '\ufffd' AND d.work < 0) AS undonePrereq, FROM item
WHERE work < 0
Can this be done in CouchDB, using a limited, small number of queries?
My closest sally is the map function
function(doc) {
if (doc.work < 0) {
var key = [];
var i;
for (i=0; i<doc._id.length; ++i)
key.push(doc._id.charCodeAt(i));
emit(key, doc.work);
}
}
and the reduce function
function(keys, values, rereduce) {
var shortestKeyLength = Infinity;
for (var i=0; i<keys.length; ++i) {
if (keys[i][0].length < shortestKeyLength)
shortestKeyLength = keys[i][0].length;
}
return [keys.length, shortestKeyLength,
keys[0][0].slice(0,shortestKeyLength), values.length];
}
A query such as
curl -X GET
'http://127.0.0.1:5984/tracker1/_design/trackerA/_view/undoneArrayNum?startkey=\[45,65,65\]&endkey=\[45,65,9999\]&group_level=2'
will return the data necessary for items at the second level, but the desired
items could be at any level.
Doug Reeder
[email protected]
http://reeder29.livejournal.com/
https://twitter.com/reeder29
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