我正在开发一个下拉菜单，该菜单使用HTML optgroups作为员工所属的组名。这是MySQL查询和输出：

mysql> SELECT employee.emp_id，employees.empname，employees.grp_id，groups.groupname FROM雇员离开的雇员加入员工组。grp_id= groups.grp_id，按组名asc排序；
+ -------- + ------------ + -------- + ----------- +
| emp_id | empname | grp_id | 组名|
+ -------- + ------------ + -------- + ----------- +
| 20 | 员工2 | 13 | 第1组|
| 19 | 员工1 | 13 | 第1组|
| 21 | 员工3 | 14 | 第2组|
+ -------- + ------------ + -------- + ----------- +
设置3行（0.00秒）

唯一的问题是，我很难确定如何使optgroup正常工作。我尝试了无数次，这真的开始让我感到沮丧。 以下是我想要的输出示例（示例）：

<select name="dropdownmenu">
    <optgroup label="Group 1">
        <option name="20">Employee 2</option>
        <option name="19">Employee 1</option>
    </optgroup>
    <optgroup label="Group 2">
        <option name="21">Employee 3</option>
    </optgroup>
</select>

基本上，optgroup必须是“ groupname”，选项“ name”应该是“ emp_id”，而动作“ option”（下拉项）是“
empname”。

我希望这是可以做的，但是真的不确定。这是我所拥有的功能，但无法正常运行：

function getDynGrpList() {
    global $db;

    // $query = "SELECT * FROM employees ORDER BY grp_id desc;";
    $query = "SELECT employees.emp_id,employees.empname,employees.grp_id,groups.groupname FROM employees left join groups on employees.grp_id = groups.grp_id order by groupname asc;";
    $employees = $db->GetAll($query);
    $groups = array();

    while ($qa = $employees->GetRows()) {
        $groups[$qa['groupname']][$qa['grp_id']] = $qa['empname'];
    }
    foreach ($groups as $label => $opt) { ?>
        <optgroup label="<?php echo $label; ?>">
<?php   }
        foreach ($groups[$label] as $id => $name) { ?>
            <option value="<?php echo $id; ?>"><?php echo $name; ?></option>
<?php } ?>
        </optgroup>
<?php }

从凌晨3:15 CST（2/27）开始的getDynGrpList函数：

function getDynGrpList() {
    global $db;

    // $query = "SELECT * FROM employees ORDER BY grp_id desc;";
    $query = "SELECT employees.emp_id,employees.empname,employees.grp_id,groups.groupname FROM employees left join groups on employees.grp_id = groups.grp_id order by groupname asc;";
    $employees = $db->GetAll($query);
    $groups = array();
    while ($qa = $employees->GetRows()) {
        $groups[$qa['groupname']][$qa['emp_id']] = $qa['empname'];
    }
    var_export($groups);
    foreach($groups as $label => $opt): ?>
        <optgroup label="<?php echo $label; ?>">
    <?php foreach ($opt as $id => $name): ?>
        <option value="<?php echo $id; ?>"><?php echo $name; ?></option>
    <?php endforeach; ?>
    </optgroup>
<?php endforeach;
}

最终解决方案（在Felix Kling的帮助下）

function getDynGrpList() {
    global $db;

    $query = "SELECT employees.emp_id,employees.empname,employees.grp_id,groups.groupname FROM employees left join groups on employees.grp_id = groups.grp_id order by groupname asc;";
    $employees = $db->GetAll($query);
    $groups = array();
    foreach ($employees as $employee) {
        $groups[$employee['groupname']][$employee['emp_id']] = $employee['empname'];
    }
    foreach($groups as $label => $opt): ?>
        <optgroup label="<?php echo $label; ?>">
    <?php foreach ($opt as $id => $name): ?>
        <option value="<?php echo $id; ?>"><?php echo $name; ?></option>
    <?php endforeach; ?>
    </optgroup>
<?php endforeach;
}