Two MySQL result sets to a nested array - php

Question

I'm having two tables of data "Item" and "Subsidiary" with the following structure:
ITEM
ItmCod
ItmName
SUBSIDIARY
ItmCodParent
ItmCodChild
I need to show a list of Items each with a list of its subsidiaries, like in this json:
{
"ItmCod":1,
"ItmName":"BogusItem1",
"Subsidiaries":
[
{
"ItmCodParent":1,
"ItmCodChild":15
},{
"ItmCodParent":1,
"ItmCodChild":16
}
]
},{
"ItmCod":2,
"ItmName":"BogusItem2",
"Subsidiaries":
[
{
"ItmCodParent":2,
"ItmCodChild":17
},{
"ItmCodParent":2,
"ItmCodChild":18
}
]
}
How can I add the second result set to the first one to have the nested as shown above. I have this code so far:
$sql = "SELECT ItmCod, ItmName FROM item";
$item_rows = array();
while($item_row = $database->fetch_array_assoc($item_result)){
$sub_sql = "SELECT ItmCodParent, ItmCodChild FROM subsidiary WHERE subsidiary.ItmCodParent = " . $item_row["ItmCod"];
$sub_result = $database->query($sub_sql);
$sub_rows = array();
while($sub_row = $database->fetch_array_assoc($sub_result)){
$sub_rows[] = $sub_row;
}
$item_rows[] = $item_row;
}
print json_encode($item_rows);
Thanks.

Answer 1

just above the line
$item_rows[] = $item_row;
simply add
$item_row['Subsidiaries']=$sub_rows;

Answer 2

I would do a single join query like this:
SELECT i.ItmCod AS ItmCod, i.ItmName AS ItmName, s.ItmCodChild AS ItmCodChild
FROM item AS i
INNER JOIN subsidiary AS s
ON i.ItmCod = s.ItmCodParent
Note I didn't select s.ItmCodParent as this is just redundant to i.ItmCod.
Then build the array like this:
$item_rows = array();
while($item_row = $database->fetch_array_assoc($item_result)){
$item_rows[(int)$item_row['ItmCod']]['ItmCod'] = $item_row['ItmCod'];
$item_rows[(int)$item_row['ItmCod']]['ItmName'] = $item_row['ItmCod'];
$sub_array = array(
'ItdCodParent' => $item_row['ItmCod'],
'ItmCodChild' => $item_row['ItmCodChild']
);
$item_rows[(int)$item_row['ItmCod']]['Subsidiaries'][] = $sub_array;
}
$item_rows = array_values($item_rows); // reset numerical indexes.
echo json_encode($item_rows);

Answer 3

I wouldn't attempt to solve this with two queries:
$sql = '
SELECT I.ItmCod, I.ItmName, S.ItmCodChild
FROM item I
LEFT JOIN subsidiary S ON (S.ItmCodParent = I.ItmCod)
';
// fetch $item_result with $sql
$item_rows = array();
while ($item_row = $database->fetch_array_assoc($item_result)) {
$cod = $item_row['ItmCod'];
if (!array_key_exists($cod, $item_rows)) {
$item_rows[$cod] = $item_row;
}
$item_rows[$cod]['Subsidiaries'] = array(
'ItmCodParent' => $cod,
'ItmCodChild' => $item_row['ItmCodChild'],
);
}
// array_values is because json_encode will keep the keys
// otherwise
print json_encode(array_values($item_rows));
That way, you aren't running an additional query for every single item row to get the subsidiaries (minimizing round-trip time, and letting the database do what it's good at).