Delete the row with the highest id in mysql, using php

Question

I'm working on a really simple minichat program ( php/mysql ) which displays the last 10 messages.

I wanted to add a button to delete the last message (using a form, leading to a php file like the one under).

I'm really a beginner with php and mysql so, I don't understand why it doesn't work.

Follows my code:

<?php 
    // Create connection
    $cn = new mysqli("localhost","root","","test");

    // Check connection
    if($cn->connect_error)
    {
        echo "Connection failed : " . $cn->connect_error;
    }

    $sql = "DELETE FROM `minichat` WHERE `minichat`.`id` = ('SELECT MAX(`id`) FROM `minichat`')";

    if($cn->query($sql) === TRUE){
            echo "Deleted succesfully";
    }
    else
    {
        echo "Error deleting record: " . $cn->error;
    }

    //header('Location: connexion.php');
?>

Answer 1

According to the manual on DELETE Syntax :

Subqueries

You cannot delete from a table and select from the same table in a subquery.

So instead you should do something like:

DELETE FROM minichat ORDER BY id DESC LIMIT 1

And you probably want a condition to make sure a user can only delete his / her own comment..

Answer 2

You should remove the single quote around the subselect

 "DELETE FROM `minichat` WHERE `minichat`.`id` = (SELECT MAX(`id`) FROM `minichat`)"

Otherwise you have WHERE minichat . id = 'mi string text'

and for fact that you can delete from a sub query you can try

 DELETE 
FROM `minichat` 
WHERE `minichat`.`id` = (select t.id from (SELECT MAX(`id`) FROM `minichat`) t)

This is expected to exceed the limit for delete with subquery

Answer 3

You could try and set up a variable which collected the ID you want. Then you can refer to that variable as the ID you want to delete.