多个SQL插入（插入的数量取决于用户输入的数量）

Question

我的网站上有一个模块，允许管理员将一些用户添加到组中。

它是这样构建的（带有选择框），您可以选择多个用户，但只能选择一个组：

Users:                       Group:
- user 1                     - group 1
- user 2                     - group 2
- user 3
- user 4
- user 5

在PHP内部，它看起来像这样：

$user_id = $_POST["user_id"]; //this can be an array
$group_id = $_POST["group_id"];

if (count($user_id) == 1) { 
    $sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id)"; 
} elseif (count($user_id) == 2) {
    $sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id), ($user_id[1],$group_id)"; 
} elseif (count($user_id) == 3) {
    $sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id), ($user_id[1],$group_id), ($user_id[2],$group_id)"; 
} elseif (count($user_id) == 4) {
    $sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id), ($user_id[1],$group_id), ($user_id[2],$group_id), ($user_id[3],$group_id)"; 
} elseif (count($user_id) == 5) {
    $sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id), ($user_id[1],$group_id), ($user_id[2],$group_id), ($user_id[3],$group_id), ($user_id[4],$group_id)"; 
} else {
    echo'Error: Too many users selected';
    exit;
}

如何用较短的代码得到它？ 也许使用准备好的语句，因为输入来自用户。

Answer 1

您是否正在寻找这样的东西？

if(count($user_id)>5){
    echo 'Error: Too many users selected';
    exit;
}
$sql = "INSERT IGNORE INTO users_groups (user_id, group_id) VALUES ($user_id[0],$group_id)";
for ( $i = 1; $i < count($user_id); $i++) {
    $sql .= ", ($user_id[$i],$group_id)"
}