multiselect query db

Question

I overthought a recent post and deleted it. Hopefully this version is a little clearer.

I have a multiselect dropdown, which I want to be able to filter a database table with.

So if I have the following drop down with roughly 70 entries:

<select multiple="multiple" id="filter" name="filter">
  <optgroup label="category1"> <!--jquery ui plugin allows for grouping -->
    <option value="sub1">Subcategory 1</option>
    <option value="sub2">Subcategory 2</option>
    <option value="sub3">Subcategory 3</option>
  </optgroup>
  <optgroup label="category2">
    <option value="sub4">Subcategory 4</option>
    <option value="sub5">Subcategory 5</option>
    <option value="sub6">Subcategory 6</option>

...

And I have 6 categories I need to search through in my sql statement, thus so far I have:

<?php
    include ("connect.php");

    $filter = $_POST["filter"];

        $result = mysql_query("SELECT * FROM edt_images
                                WHERE category1= '$filter'
                                OR category2= '$filter'
                                OR category3 = '$filter'
                                OR category4 = '$filter'
                                OR category5 = '$filter'
                                OR category6 = '$filter'")
            or die(mysql_error());
        while ($row = mysql_fetch_array($result)) {
            echo "<img src='files/small/thumb0_".$row['item_name'].".".$row['file_extension']."' border='0'/>"; 
        }
?>

Right now it works if I only select one item from the dropdown because it searches the six columns for that entry. So my question is how would I search these six columns for multiple entries?

Thanks in advance

Answer 1

If filter is an array of chosen categories you can use IN in your query:

$filterIn = implode("','",$filter);

SELECT * FROM edt_images
        WHERE category1 IN ('$filterIn')
        OR category2 IN ('$filterIn')
        OR category3 IN ('$filterIn')
        OR category4 IN ('$filterIn')
        OR category5 IN ('$filterIn')
        OR category6 IN ('$filterIn')

Note however you shouldn't be using unsanitised user input in an SQL query.

Answer 2

IMHO first of all you need to allow to return multiple values from your multiselect. To do so you need to add brackets to name attribute like so:

<select multiple="multiple" id="filter" name="filter[]">