PHP Join multiple tables not working as expected - php

Question

I'll explain briefly what I've done so far-
First of all I have multiple of stores and each store has its own table in which it contains id,item,qty and price and there is a main table called all_items that contains the total qty taken from each store table.
Now each store table either have same item number or not. Here you can see what the tables looks like :
Store tables called : S1, S2, S3
S1
id item qty price
1 x1 10 12
2 x2 10 15
3 x3 5 5
S2
id item qty price
1 x1 10 12
2 x4 6 6
S3
id item qty price
1 x3 1 5
2 x6 5 5
3 x7 5 12
all_items - Contains original total qty
id item qty price
1 x1 20 12
2 x2 10 15
3 x3 6 5
4 x4 6 6
5 x6 5 5
6 x7 5 12
Okay now, I've decided to find out the qty available for each item in all stores for comparing purposes- As follows :
item price S1 S2 S3
x1 12 10 10 -
x2 15 10 - -
x3 5 5 - 5
x4 6 - 6 -
x6 5 - - 5
x7 12 - - 5
I hope its clear for you now. I've created a form with checkbox input type ( for each store ) to allow user select which stores he wants to compare, so after submitting the form - a PHP page contains the following code :
$allstore = $_POST['store']; //Collects name from checkbox ticks under form
function createSelect($allstore)
{
if (empty($allstore))
return "";
$querySelect = "";
$queryJoin = "";
$baseTable = "";
foreach ($allstore as $store => $value) {
if (!$querySelect) {
$baseTable = "all_items";
$querySelect = "SELECT " . $store . ".item_no, " . $store . ".actual_price, " . $store . ".selling_price, " . $store . ".qty as " . $store;
} else {
$querySelect .= ", " . $store . ".qty as " . $store;
$queryJoin .= "
INNER JOIN " . $store . " ON " . $baseTable . ".item_no = " . $store . ".item_no";
}
}
$querySelect .= " FROM " . $baseTable;
$query = $querySelect . $queryJoin;
return $query;
}
$allstore = array(); // The below code allows function to know how many stores selected in $allstore
if (!empty($_POST['store'])) {
foreach ($_POST['store'] as $value) {
$allstore["s_".$value] = 0; // or 1, it doesn't matter because your function adds all the keys
}
}
var_dump(createSelect($allstore)); // Output SQL
$query = (createSelect($allstore));
$result = mysql_query($query);
//Rest of the code .....
Now if you notice $baseTable = "all_items"; makes the whole query fail. However if I change it value to $baseTable = $store; it works and shows an output but not as expected because it turns out S1 is the main now and the result will be totally different because it relays on the S1 items only.
If you can provide any helpful solution will be appreciated.

Answer 1

Why not use UNION?
function createSelect($stores)
{
$query = "";
$baseTable = "all_items";
foreach($stores as $i => $store)
{
$query .= "(SELECT {$store}.id AS {$store}_id, {$store}.item AS {$store}_item, {$store}.price AS {$store}_price, {$store}.qty AS {$store}_qty, '{$store}' as Source FROM {$store}) UNION ";
}
$query .= "(SELECT all_items.id AS {$baseTable}_id, {$baseTable}.item AS {$baseTable}_item, {$baseTable}.price AS {$baseTable}_price, {$baseTable}.qty AS {$baseTable}_qty, '{$baseTable}' as Source FROM {$baseTable})";
return $query;
}
$result = mysql_query(createSelect($allStore));
//Rest of code
//if my tables are S1, S1, and my $baseTable is bs
//echo createSelect(array('S1', 'S2'); will output (SELECT S1.id AS S1_id, S1.item AS S1_item, S1.price AS S1_price, S1.qty AS S1_qty, 'S1' as Source FROM S1) UNION (SELECT S2.id AS S2_id, S2.item AS S2_item, S2.price AS S2_price, S2.qty AS S2_qty, 'S2' as Source FROM S2) UNION (SELECT all_items.id AS all_items_id, all_items.item AS all_items_item, all_items.price AS all_items_price, all_items.qty AS all_items_qty, 'all_items' as Source FROM all_items)