In PHP, compare an array against a field in a MySQL table - php

Question

I've got two tables; one a list of location names, another a list of companies, a field of which stores potentially multiple locations that the company operates in:
id LocationName
1 Aberdeen
2 Dundee
3 Edinburgh
4 Glasgow
idCompany CompanyName Locations
1 CompanyA 1, 2, 3, 4
2 CompanyB 2, 4
3 CompanyC 1
For each company's details page, I want to list the locations in which they operate, displaying the name of each. Eg. for Company B:
Dundee
Glasgow
etc.
Coming from a VB background, I'd just loop through each dataset and compare each to find the matches, but this is in PHP and I can't get it to work:
// Query for specific firm
$sqlCompany= "SELECT * FROM company_details WHERE CompanyID='".$CompanyID."';";
$rstCompany= mysqli_query($conn, $sqlCompany);
$row = mysqli_fetch_assoc($rstCompany);
// Query list of Locations
$sqlLocationNames= "SELECT * FROM Locations ORDER BY LocationName ASC;";
$rstLocationNames= mysqli_query($conn, $sqlLocationNames);
// Explode the field of locations into an array:
$LocationArray = $row["Locations"];
$LocationArray = explode (",", $LocationArray);
for ($i = 0; $i < count($LocationArray); $i++) {
while ($rowLocationNames = mysqli_fetch_assoc($rstLocationNames)) {
if ($LocationArray[$i]==$rowLocationNames["idLocation"]) {
echo $rowLocationNames["LocationName"]."<br />";
}
}
}
Running this for Company A, I'd expect to get the list of four locations from above, but I only get the first location (Aberdeen). I've tried every combination I can think of, to no avail. I need to keep the data structured this way, as I intend having a select multiple for inserting and also editing the data when I can get this working.
Any ideas where I'm going wrong?

Answer 1

Rather than looping the database fetch inside the iteration of the array, which results in there being no data left to read once you come to the second entry in the array (and hence at most one output, as you are seeing), just loop the database fetch and use in_array to determine whether to output the location name:
while ($rowLocationNames = mysqli_fetch_assoc($rstLocationNames)) {
if (in_array($rowLocationNames["idLocation"], $LocationArray)) {
echo $rowLocationNames["LocationName"]."<br />";
}
}

Answer 2

The problem is that your while loop to read the location names from the db is nested within the for loop. After the the first iteration of the for loop, the database pointer is at the end of the recordset, so when you go through the next iteration, there are no records left to read.
Try reading the records in to an array before entering the for loop and then using the while loop to iterate over the newly created array.