使用 mysql join 显示不匹配值

Question

我有一个查询要加入 3 个表。

$this->db->select("a.user_id as id, a.plate_number as plate_number, a.current_lat as lat, a.current_lon as lon, a.created_on as created_on, a.updated_on as updated_on, a.available as available, a.location_id as location_id, b.user_name as name, b.user_email as email, b.user_phone as phone, c.name as location_name");
        $this->db->from('user_driver as a');
        $this->db->join('user as b', 'a.user_id = b.user_id');
        $this->db->join('vendor_location as c', 'a.location_id = c.location_id');
        $query = $this->db->get();
        $data['driver'] = $query->result_array();

user_driver表结构：

vendor_location 表结构：

结果：

我想显示user_driver 表的其余部分，即使没有与vendor_location 表匹配的值。 LocationName 字段可以填充 NULL 而不是根本不显示任何内容。

我尝试了left outer 和full outer，但它不起作用。它给我留下了唯一的一行显示。

Answer 1

即使没有与 vendor_location 表匹配的值，我也想显示 user_driver 表的其余部分。

为此，您应该使用LEFT JOIN。它允许您从左侧表中获取行，即使右侧表中没有匹配项。

$this->db->select("a.user_id as id, a.plate_number as plate_number, a.current_lat as lat, a.current_lon as lon, a.created_on as created_on, a.updated_on as updated_on, a.available as available, a.location_id as location_id, b.user_name as name, b.user_email as email, b.user_phone as phone, c.name as location_name");
$this->db->from('user_driver as a');
$this->db->join('user as b', 'a.user_id = b.user_id');
$this->db->join('vendor_location as c', 'a.location_id = c.location_id', 'left');//modify this line
$query = $this->db->get();
$data['driver'] = $query->result_array();

Answer 2

你试过这样吗

$this->db->join('user as b', 'a.user_id = b.user_id', 'LEFT');
    $this->db->join('vendor_location as c', 'a.location_id = c.location_id', 'LEFT');