, separated values in a variable

I have a variable $a = 271,245,789;

<select name="cat" class="main" multiple="multiple">
                    <option value="">--Select Category--</option>
                    <?
                    ////////////////display category//////////////////
                    $cat_details=mysql_query("select category_id,category from category_tb order by category");
                    while($cat_data=@mysql_fetch_array($cat_details)){?>
                    <option value="<?=$cat_data['category_id'];?>" <? if($a==$cat_data['category_id']){?> selected="selected"<? } ?>><?=$cat_data['category'];?></optio开发者_如何学运维n>
                    <? } ?>
                </select>

in mysql we have find_in_set for these "," separated values. How can i do this in PHP

Something like this?

if (in_array($value, explode(',', $a)) {
  // Found
}

OK, I know now, what FIND_IN_SET() does

$index = array_search($value, explode(',', $a));

At all with explode() you can split this CSV-string into its parts and then apply every array-function on it.

You can do this like that ($key is the position of the $value within $your_string):

$key = array_search((string)$your_value, explode(',', $your_string));

See documentation for array_search() and explode().

As alternative to the in_array/explode workaround you could also test with:

function find_in_set($set, $value) {
    return strstr(",$set,", ",$value,");
} 

Either way I would separate that out; your template is convoluted enough already. (You should really move the mysql_query out too, and provide a wrapper function which simply returns a list instead.)