Nested MySQL query in PHP

Question

I came across the following code while constructing a php file:

  $query="UPDATE EXPERTS SET ...";  
  $result=$db->query($query);         
      if ($result) 
      {     
        $query="UPDATE USERS SET ...";  
        $result=$db->query($query);     
        if ($result) 
        {       
          ...
        }
      }

My question is if the above nested query is acceptable since we use the same variable ($result). Of course, it works, however I am not sure if is there any case of creating unexpected results...

Thank you

One $result overwrites the other $result. If you're good with that, then OK. — Jay Blanchard
– Jay Blanchard, Commented Jan 28, 2015 at 15:12
There's probably nothing of value to overwrite because an UPDATE query produces only true/false as its output. There's no result set in $result (unless you are using a strange custom class) — Michael Berkowski
– Michael Berkowski, Commented Jan 28, 2015 at 15:13

Jonast92 · Accepted Answer · 2015-01-28 15:27:51Z

You can use Data Flow Anomalies for this:

Required terminology:

d($var) - Value assigned to $var or initialized.
r($var) - Value of $var read.
u($var) - Value of $var is undefined.

We wish to avoid the following patterns:

ur - A undefined value is read.
du - A variable which once had a value becomes undefined before it's read.
dd - A variable receives a new value before it's earlier value is properly used; this is probably what you're afraid of.

Now let's take a look:

$query="UPDATE EXPERTS SET ...";            
$result=$db->query($query);                        d($result)
if ($result)                                       r($result)
{     
    $query="UPDATE USERS SET ...";  
    $result=$db->query($query);                    d($result)
    if ($result)                                   r($result)
    {       
        ...
    }
}

You got two dr so we can safely assume that you got nothing to worry about; in both cases the values are assigned and read before being assigned again.

One might argue that you should make a single variable which's purpose is to indicate the result of a single query but that's up to you.

Collectives™ on Stack Overflow

Nested MySQL query in PHP

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related