sql query won't output results in php

Question

I have a drop down list script in which it is populated from the database. I'm trying to Show the name on the list, but the actual value is the ID of the name. I think it'd be better to show my code to explain what I'm trying to do:

mysql_connect('localhost', 'user', 'pw');
    mysql_select_db ("db");
    $sqlId = "SELECT id FROM materials";
    $sql = "SELECT name FROM materials";
    $result = mysql_query($sql);
    $resultId = mysql_query($sqlId);

    echo "<td><select name='materials'>";

    while ($row = mysql_fetch_array($result) && $row2 = mysql_fetch_array($resultId)) 
        {
            echo "<option value='" . $row2['id'] . "'>" . 
            $row['name'] . "</option>";
        }

    echo "</select></td></tr> ";

Every time I run this, the drop down list is never populated. What am I doing wrong?

There's no reason you need to make two SQL queries in the code. You could easily combine the two: SELECT id,name FROM materials and subsequently, in the loop, only get one result row. — snwflk
– snwflk, Commented Jan 27, 2014 at 3:48
Thanks for that. I actually just did that before checking this reply and I found that it was much shorter and looked cleaner. — remedy.
– remedy., Commented Jan 27, 2014 at 4:12

Kiel Labuca · Accepted Answer · 2014-01-27 05:34:20Z

1

I revised your code and now this should work.

mysql_connect('localhost', 'user', 'pw');
mysql_select_db ("db");

$sql = "SELECT id, name FROM materials";
$result = mysql_query($sql);

echo "<td><select name='materials'>";

while($row = mysql_fetch_assoc($result)) {
     echo "<option value='" . $row['id'] . "'>" . $row['name'] . "</option>";
}

echo "</select></td></tr> ";

Good Luck! :-)

answered Jan 27, 2014 at 5:34

Kiel Labuca

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1 Comment

remedy. Over a year ago

Yes, this is what I eventually realized what to do after looking at my code.

remedy. · Accepted Answer · 2014-01-27 03:28:57Z

0

I changed the

&&

to a "AND" within the condition and it worked.

answered Jan 27, 2014 at 3:28

remedy.

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Comments

snwflk · Accepted Answer · 2014-01-27 03:42:11Z

Your code makes wrong assumptions about operator precedence.

Here's how your while statement gets evaluated..

while ($row = (mysql_fetch_array($result) && ($row2 = mysql_fetch_array($resultId))) )

The added parentheses show the order in which PHP evaluates the loop statement. $row never holds an array of values, instead it is assigned a boolean.

Here is a simpler example:

var_dump( $x = 1 && $y = 2 );  // outputs bool(true)
var_dump( $x );  // outputs bool(true)
var_dump( $y );  // outputs int(2)

To solve, you should either rewrite your code to while (($row = mysql_fetch_array($result)) && ($row2 = mysql_fetch_array($resultId))) or, as you did, use the and operator (which has a lower precedence).

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