src/DB/Drivers/PDOSqlDriver.php
function select($fields = '*', $modifier = '')
    {
        $this->generateQueryID();
        $this->querySQL[$this->qid] = $this->SQLAssembler->select($fields, $modifier);
        $this->queryParams[$this->qid] = array();
        return $this;
    }
function select($fields = '*', $modifier = '')
    {
        $this->generateQueryID();
        $this->querySQL[$this->qid] = $this->SQLAssembler->select($fields, $modifier);
        $this->queryParams[$this->qid] = array();
        return $this;
    }
链式查询以select开始,跟原生的sql语句保持一致

@param string $fields
@param string $modifier
@return PDOSqlDriver