问题
I am developing a simple system that has unlimited categories and items in each category. For instance there could be categories inside categories etc (Category 1 -> Category 2 -> Category 3) all containing items. I want to display the total items for each category and ALL of their subcategories. I am trying to figure out a loop to do this but basically am coming up short. I am building in PHP/MySQL. My category table schema is category(id, id_parent) id being auto increment and id_parent being whether it resides inside another category (0 is default). My items schema is items(id, id_category). Obviously there are other columns but these are the only ones that matter I believe. Can someone please help me develop a loop structure come up with a total amount of items for the category they are in (counting all subcategories items as well). Here is what I started although I feel it is very, very wrong.
function CountChildDownloads($id_category)
{
global $smcFunc;
$x = array();
$total = 0;
$request = $smcFunc['db_query']('', '
SELECT COUNT(*) AS items FROM {db_prefix}xld_downloads
WHERE id_category = '.$id_category.''
);
$total += $request['items'];
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = '.$id_category.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$x[] = $row['id'];
}
}
foreach ($x as $id)
{
$y = array();
$z = 0;
$request = $smcFunc['db_query']('', '
SELECT COUNT(*) AS items FROM {db_prefix}xld_downloads
WHERE id_category = '.$id.''
);
$z += $request['items'];
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = '.$id.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$y[] = $row['id'];
}
}
while (count($y) > 0)
{
$id_y = $y[0];
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = '.$id_y.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$y[] = $row['id'];
}
}
$request = $smcFunc['db_query']('', '
SELECT COUNT(*) AS items FROM {db_prefix}xld_downloads
WHERE id_category = '.$id_y.''
);
$z += $request['items'];
unset($y[0]);
array_values($y);
}
$total += $z;
}
return $total;
}
The $smcFunc is just the systems way to do queries. It is a MySQL backend.
Working function (will need to update to standard MySQL calls if not using SMF) Thanks Lucas.
function CountChildDownloads($id_category)
{
global $smcFunc;
$x = array();
$total = array();
$total['downloads'] = 0;
$total['views'] = 0;
$request = $smcFunc['db_query']('', '
SELECT views FROM {db_prefix}xld_downloads
WHERE id_category = '.$id_category.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$total['downloads']++;
$total['views'] += $row['views'];
}
}
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = '.$id_category.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$x[] = $row['id'];
}
}
foreach ($x as $id)
{
$y = array();
$z = 0;
$w = 0;
$request = $smcFunc['db_query']('', '
SELECT views FROM {db_prefix}xld_downloads
WHERE id_category = '.$id.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$z++;
$w += $row['views'];
}
}
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = '.$id.''
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$y[] = $row['id'];
}
}
while (count($y) > 0)
{
$id_y = $y[0];
if (!empty($id_y))
{
$request = $smcFunc['db_query']('', '
SELECT id FROM {db_prefix}xld_categories
WHERE id_parent = {int:id_parent}',
array(
'id_parent' => $id_y,
)
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$y[] = $row['id'];
}
}
$request = $smcFunc['db_query']('', '
SELECT views FROM {db_prefix}xld_downloads
WHERE id_category = {int:id_category}',
array(
'id_category' => $id_y,
)
);
if($smcFunc['db_num_rows']($request) > 0) {
while($row = $smcFunc['db_fetch_assoc']($request)) {
$z++;
$w += $row['views'];
}
}
}
unset($y[0]);
$y = array_values($y);
}
$total['downloads'] += $z;
$total['views'] += $w;
}
return $total;
}
回答1:
(There are numerous approaches to nested loops / queries.. a structure change idea would be to have a separate table that lists all the children of each category.. and make sure that it not only has the immediate children, it also has the sub-children and sub-sub-children... like 1 has child 2, 2 has child 3, 1 has child 3, 3 has child 5, 1 has child 5.. etc..) BUT, for the current situation..
One loop structure could be :
Start resultset. || Query for all category ids where parent = 0. || Add each to array (X). || Close resultset.
For each id in array (X):
- Establish a new counting variable (z).
Establish a new child id array (Y).
Start resultset. || Query count * for all items with category = current id x || Add to counting variable (z) || Close resultset.
Start resultset. || Query for all category ids where parent = current id x || Add all to child id array (Y). || Close resultset.
while child array (Y) length > 0
category id y = first item in array (Y)
Start resultset. || Query for all category ids where parent = current id y. || Add all to child id array (Y). || Close resultset.
Start resultset. || Query count * for all items with category = current id y || Add to counting variable (z) || Close resultset.
remove first item from array (Y)
continue while loop
At this point you have the final item count (z) for category id x... do something with it, then continue with the for loop
End for loop
来源：https://stackoverflow.com/questions/7682781/mysql-count-all-children-no-matter-how-many-there-are