Think\Db\Query::join PHP 메소드

    public function join($join, $condition = null, $type = 'INNER')
    {
        if (empty($condition)) {
            // 如果为组数，则循环调用join
            foreach ($join as $key => $value) {
                if (is_array($value) && 2 <= count($value)) {
                    $this->join($value[0], $value[1], isset($value[2]) ? $value[2] : $type);
                }
            }
        } else {
            // 传入的表名为数组
            if (is_array($join)) {
                if (0 !== ($key = key($join))) {
                    // 设置了键名则键名为表名，键值作为表的别名
                    $table = [$key => array_shift($join)];
                    $this->alias($table);
                } else {
                    $table = array_shift($join);
                }
            } else {
                $table = trim($join);
                if (strpos($table, ' ') && !strpos($table, ')')) {
                    list($table, $alias) = explode(' ', $table);
                    $table = [$table => $alias];
                    $this->alias($table);
                }
            }
            $this->options['join'][] = [$table, strtoupper($type), $condition];
        }
        return $this;
    }

 /**
  * 附加查询表达式
  * @access protected
  * @param \think\db\Query $query 查询对象
  * @return \think\db\Query
  */
 protected static function attachQuery($query)
 {
     $master = basename(str_replace('\\', '/', get_called_class()));
     $class = new static();
     $fields = self::getModelField($master, '', $class->mapFields);
     $query->alias($master)->field($fields);
     foreach (static::$relationModel as $key => $model) {
         $name = is_int($key) ? $model : $key;
         $table = is_int($key) ? self::db()->name($name)->getTable() : $model;
         $query->join($table . ' ' . $name, $name . '.' . $class->fk . '=' . $master . '.' . $class->getPk());
         $fields = self::getModelField($name, $table, $class->mapFields);
         $query->field($fields);
     }
     return $query;
 }