Using curly brackets in multidimensional array - php

Question

I have an array of ID's used to execute mysqli queries in a foreach loop (the below code is just an example - the array will contain more than 50+ elements/ID's). For each array element/ID I query an array which I then include in a compData array. However, I am unsure of how to dynamically define the arrays in the foreach loop. I would very much appreciate if you can check whether I am using ${$val} correctly in the below or if something else is wrong. Thanks.
$idArray = array(
"List1",
"List2",
);
$compData = array();
foreach($idArray as $val) {
$sth = mysqli_query($conn, "SELECT * FROM {$tableName} WHERE ID = {$val}");
${$val} = array();
while($r = mysqli_fetch_array($sth)) {
For ($n = 1; $n <= $CI_NOYEARS; $n++){
${$val}['data'][] = $r[$n];
}
}
$compData[{$val}] = ${$val}
}
foreach($compData['List1'] as $result) {
For ($n = 0; $n <= $CI_NOYEARS; $n++){
echo $result[$n];
}
}
The above code does not work and does not echo any data from the $compData array. Below is an example that works just fine where I execute the code using the ID's directly.
$sth = mysqli_query($conn, "SELECT * FROM {$tableName} WHERE ID = 'List1'");
$List1 = array();
while($r = mysqli_fetch_array($sth)) {
For ($n = 1; $n <= $CI_NOYEARS; $n++){
$List1['data'][] = $r[$n];
}
}
$companyData = array();
$companyData['List1'] = $List1;
foreach($compData['List1'] as $result) {
For ($n = 0; $n <= $CI_NOYEARS; $n++){
echo $result[$n];
}
}

Answer 1

It's a bit tough figuring out what your goal is based on the code you provided, but it seems far more complicated than it needs to be. I think what I've got here will replicate your desired output.
You should also be using prepared statements; they are safer, and take a lot of the overhead out of database queries when you're going to be repeating the same query multiple times. I've implemented them here.
$idArray = ["List1", "List2"];
$sth = $conn->prepare("SELECT * FROM `$tableName` WHERE ID = ?");
foreach($idArray as $val) {
$data = [];
$sth->bind_param("s", $val);
$sth->execute();
$result = $sth->get_result();
while ($r = $result->fetch_array()) {
$data = array_merge($data, array_splice($r, 1, $CI_NOYEARS));
}
$compData[$val]["data"] = $data;
}
foreach($compData["List1"]["data"] as $result) {
echo $result;
}

Answer 2

I don't understand why you're using that curly-brace notation at all when you're just copying it over into a multidimensional compData array anyway? Why not just directly put the data into the array:
for ($n = 1; $n <= $CI_NOYEARS; $n++) {
$compdata[$val]['data'][] = $r[$n];
}
(You'll also need to declare it as an array at the top level of the foreach of course.)
Side note: I would suggest not interpolating data directly into your query string like that, and instead using bound parameters: http://php.net/manual/en/mysqli-stmt.bind-param.php It's much more secure.