core/SqlSelector.php
public function where($sql = null, $args = null)
    {
        if ($sql === null) {
            return $this;
        }
        $this->condition->where($sql, $args);
        return $this;
    }
public function where($sql = null, $args = null)
    {
        if ($sql === null) {
            return $this;
        }
        $this->condition->where($sql, $args);
        return $this;
    }
条件查询
@param null $sql
@param null $args
@return $this