PHP wait for MYSQL to finish query

Question

I have to run mysql query in a for loop like this

$date_start = '2017-01-01';
$date_end = '2017-01-10';
while ($date_start < $date_end){
   $sql ("SELECT id FROM mytable WHERE mydate = '$data_start'"); [<--edit]
   $result = $db->query($sql);
   $f = $result->fetch();
   echo 'result is : '.$f['id'];
   $date_start = date('Y-m-d', strtotime($date_start. ' + 1 days'));
}

ID result was always related to first $date_start, then first sql query...

How to wait php for mysql to finish query?

EDIT.:

Ok, there was a mistake when I create the loop here, but is a distraction! It's not a copy/paste

After this I wrote

ID result was always related to first $date_start, then first sql query...

This means that is not a code problem, the loop works, else I have a php error!

I will try with MYSQL error reporting

Simply look at the highlighting colour. There is an obvious string literal issue in this code — RiggsFolly
– RiggsFolly, Commented Feb 9, 2017 at 21:52
PHP will always "wait" for a query to finish before it continues executing the script. That is how PHP works, nothing you have to take care of. — arkascha
– arkascha, Commented Feb 9, 2017 at 21:55

RiggsFolly · Accepted Answer · 2017-02-09 22:11:39Z

You have a string literal that is not closed properly, and the assignment of the query to the variable $sql is incorrect. Therefore the script is crashing

// while testing specially if you are developing on a live server
// that will have error reporting to the screen turned off
// add these 4 lines so you see your errors on the browser page
ini_set('display_errors', 1); 
ini_set('log_errors',1); 
error_reporting(E_ALL); 
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

$date_start = '2017-01-01';
$date_end = '2017-01-10';
while ($date_start < $date_end){
    $sql = "SELECT id FROM mytable WHERE mydate = '$data_start'";
    // --new character added to close the literal------------->^
    // () removed
    $result = $db->query($sql);
    // check for errors
    if ( !$result) {
        echo $result->error;
        exit;
    }
    $f = $result->fetch();
    echo 'result is : '.$f['id'];
    $date_start = date('Y-m-d', strtotime($date_start. ' + 1 days'));
}

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