用php代码更新phpmyadmin中的记录

Question

I have a reservation form where once it is filled out, the rooms available for a certain building are decreased by one. I am using Cloud9 ide with php to update the record for that building in the phpmyadmin database. I think the equation to subtract one room from roomsAvailable is not being read. It might be as simple as an issue with quotes.

This is the update:

$sql = "UPDATE $dormTable SET roomsAvailable = --$dormRecord[roomsAvailable] 
        WHERE id = $dormRecord[id]";

This is the output on the webpage when i echo the statement and the dorm record:

"UPDATE `dorms` SET `roomsAvailable` = --5 WHERE `id` = 8"

Array ( [id] => 8 [name] => Lower West Cedar St. [class] => 2 [specialNeeds] => 1 [laundry] => 1 [fullyEquippedKitchen] => 1 [roomsAvailable] => 5 [roomsReserved] => 0 [roomCapacity] => 5 )

Answer 1

我认为这将是更好的解决方案

$sql = "UPDATE dorms  SET roomsAvailable = roomsAvailable-1 WHERE id = $dormRecord[id]";

Answer 2

If you need the value of --$dormRecord[roomsAvailable] you shuold use string concatenation for $sql

In this way the php code is execute and the result is concatenated with query

$sql = "UPDATE $dormTable SET roomsAvailable = "  .  --$dormRecord[roomsAvailable]  .
     "  WHERE id = $dormRecord[id]";

you can see thye result using

echo  $sql ;