Get selected values in multiselect form field - php

Question

I'm updating a PHP form field from a dropdown (single value selected) to a multiselect (multiple values selected).
I have 2 DB tables, one where the complete list of team members reside, and the other where the selected team members reside.
On the PHP page, I want to get the values from the full team members table and show the full list as a multiselect form field.
Then I want to be able to get the values from the selected team member table and have them show as selected options in the full multiselect list mentioned above.
Any idea on how I would accomplish this?
Here's my code, although right now it just returns the full team member list without the selected values.
$query = "SELECT walkername FROM Team_Management WHERE active=1 ORDER BY walkername ASC";
$stmt = $mysqli->prepare($query) or die ("Couldn't execute query: ".mysqli_error($mysqli));
$stmt->execute();
$stmt->bind_result($walkers);
echo "<div class='form-group'>";
echo "<label class='col-lg-3 control-label' for='Walkers'>Walkers:</label>";
echo "<div class='col-lg-5'>";
echo "<select multiple class='form-control' name='walkers[]' id='Walkers'>";
while ($stmt->fetch()) {
echo "<option value='$walkers'>$walkers</option>";
}
echo "</select>";
echo "</div>";
echo "</div>";
$stmt->close();
** UPDATED **
So one thing that I should've added, is that the SELECTED_TEAM_MEMBERS field is a comma separated field.
TEAM_MANAGEMENT table
id || walkername
1 || John
2 || Kate
SELECTED_TEAM_MEMBER table
cid || walkers
1 | John,Ray,Kate
2 | Kate,Matt,Joe
In addition, each group in the walkers field in the SELECTED_TEAM_MEMBER table is tied to a unique client id (cid).
So how can I identify the selected walkers from the complete list in the TEAM_MANAGEMENT table by unique client id.

Answer 1

You can get the list of your selected user with a boolean in your SQL request
SELECT walkername,
CASE WHEN **selected_team_members_name** > '' THEN '1' ELSE '0' END as is_selected
FROM Team_Management
LEFT OUTER JOIN **SELECTED_TEAM_MEMBERS** ON **selected_team_members_name** = walkername
WHERE active=1
ORDER BY walkername ASC
With selected_team_members_name the name of the column in your table and SELECTED_TEAM_MEMBERS the name of your table
And now $walker is as array with 2 key: walkername and is_selected
And after you can try a if to put them the attribute 'selected' when you write your 'option' tag
while ($stmt->fetch())
{
$selected = "";
if($walkers['is_selected'] == '1'){ //If your walker is selected
$selected = "selected";
}
echo "<option ".$selected." value=".$walkers['walkername'].">".$walkers['walkername']."</option>";
}
I may not have understand the context but i hope i helped you.