PHP While循环中的While循环

Question

I've had this problem for a little while and probably didn't ask the question properly last time. Having dabbled again I'm still very much confused and stuck.

I have a MySQL table that I list out a series of checkboxes based on values in this (around 200).

I have another MySQL table where a user will store their preferences, when the list loads I wish for the items that the user had previously selected in the second MySQL table to be checkboxes that have the check mark already assigned indicating previous choice. If you could please take a look at the following and point me in the right direction I'd be grateful.

$result = mysql_query("SELECT `car` FROM `carlist` ORDER BY variety ASC");
$result2 = mysql_query("SELECT `car` FROM `lists` WHERE `username` = 'Palendrone' ORDER BY variety ASC");

if (!$result) {
    die("Query to show fields from table failed");
}

if (!$result2) {
    die("Query to show fields from table failed");
}

$fields_num = mysql_num_fields($result);
for($i=0; $i<$fields_num; $i++)
{
    $field = mysql_fetch_field($result);
}


$fields_num2 = mysql_num_fields($result2);
for($j=0; $j<$fields_num2; $j++)
{
    $field2 = mysql_fetch_field($result2);
}

while($row = mysql_fetch_row($result))
{

    while($row2 = mysql_fetch_row($result2))
    {

        if("$row2[0]" <> "$row[0]")
        {?><input type="checkbox" value="<?php echo "$row[0]"?>" name="<?php echo "$row[0]"?>" id="<?php echo "$row[0]"?>">
            <label for="<?php echo "$row[0]"?>"><?php echo "$row[0]"?></label>
            <?php
        } else
        {?><input type="checkbox" value="<?php echo "$row[0]"?>" name="<?php echo "$row[0]"?>" checked="yes" id="<?php echo "$row[0]"?>">
            <label for="<?php echo "$row[0]"?>"><?php echo "$row[0]"?></label>
            <?php
        }

    } /* end while */

} /* end while */

I figured the first While loop to load the main 200 items in, then for each input in that table it cross checks against the users selection table in the second while loop, in that loop I have the if statement working in reverse order so as not to check it then uncheck it.

I was pointed in the way of starting from scratch last week by another user on here, although I've started going through some tutorials I kinda need to get this last part of my project nailed...

Answer 1

I would suggest changing your query strategy - use only one instead of two. You can check the value of second member of select list - lists . car from result of query below for null value. If it is null then checkbox is not selected otherwise it is (it is present in second table).

$result = mysql_query("SELECT `carlist`.`car`, `lists`.`car`  FROM `carlist` left join `lists` on (`carlist`.`car` = `lists`.`car` and `lists`.`username` = 'Palendrone') ORDER BY `carlist`.variety ASC");