Question

I’ve got a SQL query within a foreach loop. Sometimes there can be many, and I mean a lot of queries to do, depending on several criteria, up to 78 queries potentially.

Now, I know that premature optimisation is root cause of all evil, but I don’t want to see 78 queries – it’s just not healthy.

Here’s the code:

$crumbs = explode(",", $user['data']['depts']);

foreach ($crumbs as &$value) {
    $data = $db->query("SELECT id FROM tbl_depts WHERE id = '" . $value . "'");
    $crumb = $data->fetch_assoc();
    $dsn = $db->query("SELECT msg, datetime FROM tbl_motd WHERE deptid = '" . $value . "'");
    $motd = $dsn->fetch_assoc();
    if ($motd['msg'] != "") {
        <?php echo $motd['msg']; ?>
    }
}

Can I make it any better?

Answer 1

Use IN MySQL operator to search over a set of values for id:

$ids = '"' . implode('", "',$crumbs) . '"';
$query1 = "SELECT id FROM tbl_depts WHERE id IN (" . $ids . ")";
$query2 = "SELECT msg, datetime FROM tbl_motd WHERE deptid IN (" . $ids . ")";

And so you will not need to retrieve all data you need using foreach loop, so you will have only 2 queries instead of 78.

Example: I have a table named table with 10 records which ids are: 1,2,3,4,5,6,7,8,9,10 (auto-incremented). I know I need records with ids 1,5,8. My query will be:

$sql = "SELECT * FROM `table` WHERE id in (1,5,8);";

And I don’t understand why do you need to use & operator in foreach loop if you don’t modify the $crubms arrays values.