Delete function not working PHP MySQL

Question

I have the following DELETE function i've tried to write by hand, from what I've learnt so far, however it doesnt seem to be working and I cant find anything online to see where im going wrong, can anybody see obvious errors?

<?php 
if(isset($_POST['int1'])) { 
    $interest = $_POST['int1']; 
    mysql_query = ("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID();
}
elseif(isset($_POST['int2'])) {
    $interest = $_POST['int2']; 
    mysql_query = ("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID();
} 
elseif(isset($_POST['int3'])) {
    $interest = $_POST['int3']; 
    mysql_query = ("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID();
}

print $interest1 . "<form method='post' action='#'><input type='hidden' value='".$interest1."' name='int1' id='int1'/><input type='submit' value='delete' /></form><br />";
print $interest2 . "<form method='post' action='#'><input type='hidden' value='".$interest2."' name='int2' id='int2'/><input type='submit' value='delete' /></form><br />";
print $interest3 . "<form method='post' action='#'><input type='hidden' value='".$interest3."' name='int3' id='int3'/><input type='submit' value='delete' /></form><br />";
?>

Now trying this with no luck...

    <?php 
    if(isset($_POST['int1'])) { 
        $interest = $_POST['int1']; 
        $qResult= mysql_query("UPDATE user_interests SET interest = null WHERE interest = $interest and user_id = ". mysql_real_escape_string($usersClass->userID()));
    }
    elseif(isset($_POST['int2'])) {
        $interest = $_POST['int2']; 
        $qResult= mysql_query("UPDATE user_interests SET interest = null WHERE interest = $interest and user_id = ". mysql_real_escape_string($usersClass->userID()));
    } 
    elseif(isset($_POST['int3'])) {
        $interest = $_POST['int3']; 
        $qResult= mysql_query("UPDATE user_interests SET interest = null WHERE interest = $interest and user_id = ". mysql_real_escape_string($usersClass->userID()));
    }

    print $interest1 . "<form method='post' action='#'><input type='hidden' value='".$interest1."' name='int1' id='int1'/><input type='submit' value='delete' /></form><br />";
    print $interest2 . "<form method='post' action='#'><input type='hidden' value='".$interest2."' name='int2' id='int2'/><input type='submit' value='delete' /></form><br />";
    print $interest3 . "<form method='post' action='#'><input type='hidden' value='".$interest3."' name='int3' id='int3'/><input type='submit' value='delete' /></form><br />";
    ?>

Have you tried executing the delete statements by hand to see if they work? Have you verified that the IDs (the int1, int2, int3) are valid and refer to a record in the table? — FrustratedWithFormsDesigner
– FrustratedWithFormsDesigner, Commented Jul 7, 2011 at 20:56
to fix this kind of error you just need to read what parser tells you.... — dynamic
– dynamic, Commented Jul 7, 2011 at 21:00

Brad · Accepted Answer · 2011-07-07 20:57:23Z

5

You can't do mysql_query =, as mysql_query() is a function. Try this instead:

$qResult= mysql_query("DELETE " . mysql_real_escape_string($interest) . "FROM user_interests WHERE user_id = " . mysql_real_escape_string($usersClass->userID()));

Plus, you're wide open to SQL injection. You should consider using PDO with prepared queries to avoid this issue. At a minimum, use mysql_real_escape_string() as I show you here.

answered Jul 7, 2011 at 20:57

Brad

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1 Comment

Parris Varney Over a year ago

I don't think this will work unless $interest = LOW_PRIORITY, QUICK, or IGNORE

locrizak · Accepted Answer · 2011-07-07 20:58:37Z

0

Might be a typo but not sure what you error is in the first place but for starters you are missing a close ) on all of the mysql_query calls and it would be $result = mysql_query(

$result = mysql_query("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID());

answered Jul 7, 2011 at 20:58

locrizak

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Comments

beardhatcode · Accepted Answer · 2011-07-07 20:58:41Z

0

if you wan't to excute it must be:

mysql_query("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID());

btw: doesn't this give a synaxis error?

mysql_query = ("DELETE $interest FROM user_interests WHERE user_id = ". $usersClass->userID();

the first '(' is not clossed

answered Jul 7, 2011 at 20:58

beardhatcode

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Comments

Brian · Accepted Answer · 2011-07-07 21:00:19Z

0

To delete a row in MySQL, you don't specify anything between DELETE and FROM. It should look like this:

DELETE FROM table_name WHERE some_column = some_value

answered Jul 7, 2011 at 21:00

Brian

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2 Comments

Liam Over a year ago

So how would I specify the user ID? Lots of users have the same interests

Brian Over a year ago

If you specify the user id, there will only be one row outputted.

Shauna · Accepted Answer · 2011-07-07 21:01:04Z

0

In addition to the other answers, you're not using it correctly. Your $interest shouldn't be there, unless it's one of the keywords. If it's not one of the keywords, the statement should just be delete from ....

If you're looking to change the value of a field (even deleting the contents), you'll need an update statement, instead. Something like UPDATE table SET field1 = null WHERE user_id = $uid.

answered Jul 7, 2011 at 21:01

Shauna

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Comments

Parris Varney · Accepted Answer · 2011-07-07 21:59:04Z

0

I'm not sure what $interest is, but it doesn't belong in between DELETE and FROM. DELETE deletes a whole row, not specific parts for a row. mysql_query is a function as well, so you shouldn't have that '=' in there.

Try:

 mysql_query('DELETE FROM user_interests WHERE user_id = '. $usersClass->userID();

Also, I'm not sure I agree with the comments saying you're vulnerable to sql injection, if the end user can control what is sent in their user ID, then you'll be fine. Just so long as you don't put that $interest variable anywhere in your query.

Regarding your new code, you'll want to escape $interest this time, it's something the user is submitting. If $interest or userID are non-numeric or begin with leading 0s, you need to put single quotes around them. I'd also try printing $usersClass->userID(), it might not be returning what you expect.

edited Jul 7, 2011 at 21:59

answered Jul 7, 2011 at 21:05

Parris Varney

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1 Comment

Liam Over a year ago

Thanks PMV, the usersClass->User id is correct so I know its not that, Each user has a row in the table consisting of "ID, user_id, interest) I need to somehow delete whatever row contains the interest deleted, if this makes sense?

Liam · Accepted Answer · 2011-07-07 22:19:28Z

0

Ive finally found the problem, Firstly I used 'or die()' to see where I was going wrong (I SHOUDL ALWAYS DO THIS!)

I then received the error 'unknown column in where clause' which led me to add '' around my var, the final query is...

$qResult= mysql_query("DELETE from user_interests WHERE interest = '" . mysql_real_escape_string($interest) . "' and user_id = " . $usersClass->userID());
if(! $qResult )
    {
      die('Could not delete data: ' . mysql_error());
    }

answered Jul 7, 2011 at 22:19

Liam

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