Question

I am developing an application that updates data in a table based on values selected from another table. I had searched the net,a nd tried to modify some samples to fit my needs, but still not working.

Below is some of my code:

$sync_2 = "
  select pin,ddt_1
  from purchases
  where (amount_to_repay-amount_repaid)>0
    and status like 'U%'
    and counter=1
";
$sync_2_res = mysqli_query($link, $sync_2);
$row = mysqli_fetch_assoc($sync_2_res);
$data = mysqli_num_rows($sync_2_res);

$i;
for ($i = 0; $i <= $data; $i++) {
  $pin = $row['pin'];
  $ddt = $row['ddt_1'];
  $sql = "
    update deductions
    set amount = '$ddt_1'
    where pin = '$pin';
  $result = mysqli_query($link,$sql);
}

Nothing is getting populated. Do I have to change the type of loop?.

Answer 1

Try this code, which should do the whole operation in a single query:

$query = "
  UPDATE `deductions` `d`
  JOIN `purchases` `p` ON `p`.`pin` = `d`.`pin`
  SET `d`.`amount` = `p`.`ddt_1`
  WHERE
    (`p`.`amount_to_repay` - `p`.`amount_repaid`) > 0
    AND `p`.`status` LIKE 'U%'
    AND `p`.`counter` = 1
";
$result = mysqli_query($link, $query);